Appellants in these criminal jury cases were convicted of violating 18 U.S.C. § 751(a) (1976)1 by escaping “from the custody of the Attorney General” when they departed from the New Detention Center of the District of Columbia Jail (“Northeast One”) in the early morning hours of August 26, 1976. Appellants Bailey and Walker had been brought from federal prisons where they were serving sentences for federal crimes to the D.C. Jail pursuant to writs of habeas corpus ad testificandum issued by the Superior Court of the District of Columbia2; appellant Cooley was serving a sentence in the D.C. Jail for a federal crime. Appellants raise various issues, both individually and in common, but only two *1091require extended discussion 3: whether the trial court erred in refusing to let the jury consider whether evidence of threats, assaults, and conditions in the jail either negated the intent required to commit the crime of escape or provided a defense of duress, and whether the prosecution’s evidence and the trial court’s instructions were adequate on the issue of whether appellants were in the custody of the Attorney General by virtue of the convictions alleged in the indictment. We conclude that appellants are entitled to a new trial because the trial court did not properly instruct the jury as to what constitutes an “escape” and excluded relevant evidence from the jury’s consideration. We also find that the trial court’s instructions on the custody element were in some respects confusing and potentially misleading, but these problems will presumably be corrected in the new trial.
I
Appellants first contend that the trial judge erred in refusing to let the jury consider certain allegedly exculpatory evidence. The evidence in question sought to establish that there were frequent fires in the D.C. Jail where appellants were confined, set by both inmates and guards, and often allowed to burn while the inmates suffered from lack of proper ventilation,4 that appellants had been threatened with physical violence by guards,5 that appellants Bailey and Cooley had actually been beaten by guards,6 that appellant Walker had epilepsy and had received inadequate medical treatment for his condition,7 and that appellant Cooley had been forced by his co-appellants to leave the jail.8 Appellants argued in the District Court and assert again on appeal that this evidence was relevant either as negating the specific intent they claim is required as an element of the crime of escape or as establishing a defense of duress.
The trial court admitted this evidence during the trial, but effectively precluded the jury from considering it with regard to intent by holding that the crime of escape requires only general, rather than specific, intent.9 The court also refused to allow the jury to consider the defense of duress, holding that the duress defense is available only when the person asserting it turns himself in, and that this prerequisite was absent in appellants’ cases as a matter of law.10
*1092A. Intent
Our consideration of the relevance of the evidence in question to the elements of the crime of escape under 18 U.S.C. § 751(a) leads us to agree with the Seventh Circuit in United States v. Nix, 501 F.2d 516 (7th Cir. 1974), that a great deal of unnecessary confusion has been generated by the use of ill-defined terms and concepts such as “specific” and “general” intent.11 Much of this unhelpful complexity can be avoided by returning to basic principles — beginning with a clear definition of the crime of escape and proceeding to consider the proper roles of prosecution, defense, court, and jury in trying escape cases.
Consciously ignoring labels such as “specific” and “general” intent, the court in Nix concentrated on “what constitutes the ‘escape’ element of the crime.” 501 F.2d at 518. Although “escape” is usually treated as a single element of the offense defined in Section 751(a), the word “escape” — like many other legal terms12 — is not self-defining. A jury needs more instruction than this one word if it is properly to consider whether a defendant has “escaped.” The Seventh Circuit found that “[m]ost courts, confronted with evidence that a defendant could not or did not form an intent to leave and not to return, have held such an intent essential to proof of the crime of escape.” Id. (emphasis added).13 The court then concluded that this “close to unanimous” approach of the courts was justified by “the desire to have one human element of ‘blameworthiness’ as a basis for punish*1093ment”14 and because “a prisoner who has no intent to escape — because he is grossly intoxicated, or thinks his jailer has told him to leave, or mistakes the boundaries of his confinement, or has a gun held to his head by another inmate — is not likely to endanger society, as a wilful escapee is.” Id. at 519.
On the basis of its review of precedents and policies, the Seventh Circuit defined “escape” for purposes of Section 751(a) as “a voluntary departure from custody with an intent to avoid confinement.” Id. Following the Seventh Circuit’s analysis, we conclude that an “escape” occurs when a defendant (1) leaves custody (2) voluntarily,15 (3) without permission,16 and (4) with an intent to avoid confinement.17
In order to convict a defendant of escape, the prosecution must prove each of these factors beyond a reasonable doubt. In the ordinary case the prosecution can *1094establish a prima facie ease that a defendant “escaped” by offering evidence that the defendant departed from custody without permission. Absent any additional evidence introduced by the defendant, such a case can be submitted to the jury with the instruction that the jury may infer the defendant’s intent from the circumstances.18 The defense has the opportunity, however, to submit additional evidence tending to negate any essential aspect of the offense. For example, a jury can consider whether evidence of jail conditions, threats, and violence such as that presented by appellants in the District Court raises reasonable doubts concerning a defendant’s capacity to act “voluntarily,” or his intent to avoid confinement.19
The prosecution then has the opportunity to rebut the defense’s evidence. The prosecutor can offer evidence of any circumstances or behavior inconsistent with the defendant’s exculpatory contentions. Depending on that evidence, a prosecutor may argue that the conditions allegedly necessitating the defendant’s departure from custody were relatively mild, that alternative remedies short of escape (e. g., resort to prison authorities or the courts) were available, or that the defendant failed to return voluntarily to custody once the conditions allegedly motivating the escape no longer threatened him. If the defendant takes the stand in his own defense, the prosecutor can inquire why he did not return voluntarily and can test the credibility of his defense by the rigors of cross-examination.
Finally, when instructing the jury on the elements of the offense charged, the judge should direct the jurors’ attention to those considerations that require special emphasis. In addition to specifying the major indicia of voluntariness and intent — the immediacy, specificity, and severity of any alleged threats or fears, the availability of viable alternatives to unauthorized departure, and the defendant’s decision whether and when to return to custody — the court should remind the jury of the inevitable difficulties associated with prison discipline20 and of the possible biases of defense and prosecution witnesses testifying with respect to that aspect of the case.21 It is the jury, however, that must make the final determination whether the prosecution has met its burden of proving each of the elements of the crime beyond a reasonable doubt. The court may not, as the District Court did in this case, take upon itself the responsibility for making this determination.
Our analysis of the law of escape indicates that the District Court erred in its definition of the offense and consequently precluded the jury’s consideration of evidence that was relevant to an essential element of the crime. The trial judge instructed the jury that a defendant “escaped” if he “without authorization did absent himself from his place of confinement.” Tr. 802. Relying on the opinion of the Tenth Circuit in United States v. Woodring, 464 F.2d 1248, 1251 (10th Cir. *10951972), the trial judge told the jury that only a “general intent” was required to commit the crime of escape, and that this “means only that a defendant has the purpose to do something, the will to do the act. It means the act was done consciously and not inadvertently or accidentally.” Tr. 803. Woodring is weak authority for the proposition that escape under 18 U.S.C. § 751 requires only “general” intent, since the court’s entire “discussion” of the issue is limited to the following cryptic and conclu-sory reference:
The instruction on specific intent is. not erroneous where willfulness is in the indictment. Even though specific intent is not an element of § 751(a), specific intent became the law of the case when the Court gave Instruction 11 [“specific intent must be proved before there can be a conviction”]. * * *
464 F.2d at 1251 (emphasis added).22 As indicated above, we find the Seventh Circuit's careful analysis in United States v. Nix much more persuasive authority.23
The District Court’s attachment to a definition of “escape” that would effectively prevent the jury from considering the evidence of conditions in the jail, assaults, and threats in relation to appellants’ intent reflects a line of cases in which courts, moved by fears of undermining prison discipline or encouraging mass escapes, have hesitated to allow juries even to consider such allegedly exculpatory evidence in escape cases unless various rigorous conditions have been satisfied.24 We find no adequate justification *1096for this special broad proscription against admission of such probative defense evidence relating to intent. Juries are accustomed to determining the intent of alleged criminals, and we see nothing in the context of prosecutions for escape that requires the court to risk denying the defendants a fair trial by denying the jury its normal function. Those escape cases in which juries have been allowed to consider exculpatory evidence offer no support for fears that jurors are unable reasonably to consider all the aspects of escape cases or that juries will render decisions that will “encourage” escapes.25 In fact, the assumptions underlying the special restrictions on defense evidence in escape cases appear to be pure speculations without any empirical support in either the case law or the scholarly literature. On the other hand, the pernicious consequences of the restrictive rules are all too clear from the reported cases.26 As we have explained above, the proper approach is to inform the jury of those considerations that are relevant to its deliberations, not to take the issue out of its hands.27 In our view allowing the jury to perform its accustomed role in escape cases may make those responsible for prison conditions more conscious of their responsibilities and may well lead to fewer, rather than more, escapes. See People v. Harmon, 53 Mich.App. 482, 220 N.W.2d 212 (1974), aff’d, 394 Mich. 625, 232 N.W.2d 187 (1975).28 See also United States v. United States Gypsum Co., - U.S. -,---, 98 S.Ct. 2864, 2872-2878, 57 L.Ed.2d 854 (1978).
B. Duress-Necessity-Compulsion-Choice of Evils-
In addition to giving an instruction that made the evidence of conditions in the jail, assaults, and threats irrelevant to the intent issue, the trial judge refused to let the jury consider the evidence as grounds for a defense of “duress.” There is some theoretical confusion over the nature of the defenses of duress and necessity, especially in the context of prison escape cases.29 This confusion can be minimized, *1097however, by concentrating on the basic principles underlying a proffered defense and avoiding unhelpful labels such as “duress” and “necessity.”
The defenses usually raised under the duress/necessity labels reflect two different general principles of exculpation. One of these principles, exemplified by the notion of duress as compulsion, dictates that a person will not be held responsible for an offense he commits under threats or conditions that a person of ordinary firmness would have been unable to resist.30 This principle, like the defenses of intoxication, insanity, and mistake, negates the intent or voluntariness elements of an offense.31 Instructions with respect to this type of defense for the crime of escape are discussed above under “Intent” (I-A supra) and require no further consideration here.32
The other general principle reflected in the discussions of duress/necessi*1098ty defenses is one of justification by choice of the lesser evil — i. e., that a person is not guilty of an offense if he committed it because he reasonably believed his action was necessary to avoid a harm more serious than that sought to be prevented by the statute defining the offense.33 Rather than excusing a defendant’s action because he lacked the intent society wishes to punish, this “choice of evils” defense affirmatively justifies the defendant’s action: the defendant did the right thing, because “public policy favors the commission of a lesser harm (the commission of what would otherwise be a crime) when this would avoid a greater harm.” 34 Courts and legislatures that have recognized this type of defense have often reflected the theoretical confusion surrounding the duress/necessity labels more than the fundamental choice of evils principle by creating “fixed rules which depart somewhat from the rationale underlying the [general] rule.”35 The tendency of courts to structure duress/necessity defenses in terms of such fixed rules has been particularly pronounced in escape cases.36 The more progressive codes and cases, however, have tended to reduce the theoretical and practical complexities of the choice of evils defense to a few general guidelines consistent with its basic rationale.37 *1099ly supported39 choice of evils defense in the absence of one of the special prerequisites some courts have imposed upon such defenses in escape cases- — the requirement that an escapee turn himself in to the authorities immediately after escaping.40 After considering appellants’ proposed “duress” instruction41 and a memorandum on duress/necessity defenses in escape cases submitted by the Government42 the trial court announced that it had prepared an instruction on duress, but at the last moment decided that it could not give the instruction because, “[a]s the Court heard the evidence,” the defendants had not turned themselves in or made adequate efforts to do so. Tr. 806 — 807.43
*1098In regard to the choice-of-evils-type defense, this particular case in its present posture at most38 presents the relatively narrow question whether a jury should be allowed to consider an otherwise sufficient-
*1099The most influential statement of the “return requirement” as a prerequisite to a choice-of-evils-type defense in escape cases is contained in the opinion of an intermediate California appellate court in People v. Lovercamp, 43 Cal.App.3d 823, 118 Cal.Rptr. 110 (1974).44 The Lovercamp court apparently imposed the requirement because it feared that without it a prisoner who satisfied the other conditions of the defense could “thereafter go his merry way relieved of any responsibility for his unseemly departure.” 118 Cal.Rptr. at. 115. Subsequent opinions, most notably the Ninth Circuit’s discussion in United States v. Michelson, 559 F.2d 567 (9th Cir. 1977),45 have developed this rudimentary rationale more rigorously. The Michelson court’s analysis reveals that the return requirement is based on the critical assumption that escape is a “continuing” offense, i. e., that one may commit the crime of escape, even if his original departure from custody was justified, by failing or refusing to return to custody once the justifying circum*1100stance is no longer present. Thus the Ninth Circuit found it unnecessary to decide “whether defendant acted out of duress in escaping” because the defendant in Michelson had been absent from custody for nearly two years and his duress defense applied only to his initial departure, not to the two years he was at large.46 559 F.2d at 571. In support of its conclusion the Michelson court cited with approval United States v. Chapman, 455 F.2d 746 (5th Cir. 1972), where “[t]he jury was instructed that even if they should find that the defendant was initially forced by other prisoners to leave federal custody, ‘if he thereafter on his own volition decided to remain at large this would constitute the crime of escape.’ ” 559 F.2d at 570-571, quoting United States v. Chapman, supra, 455 F.2d at 749 (emphasis added). Under the analysis in these cases, the return requirement merely stands for the limited and commonsense notion that a choice of evils defense to the crime of “escape” — defined as leaving and staying away from custody — lasts only as long as the choice of evils justifies a failure to return.
The Ninth Circuit’s analysis indicates that the trial court’s application of the return requirement in the circumstances of this case was inappropriate.47 Even if we accept the notion on which the requirement is based — that escape is a continuing offense — this theory was not reflected in the indictment or in the trial court’s charge to the jury. Although we would be very sympathetic to a jury instruction similar to that in Chapman to the effect that a defendant can “escape” by failing to return to custody even if his initial departure was justified and that a choice of evils defense to escape must therefore justify not only a defendant’s original departure but also his continued absence,48 no such instruction was given in this case. Instead, appellants were indicted for “flee[ing] and escaping]” “[o]n or about August 26, 1976,” 49 and the trial court’s instructions, rather than explaining a “continuing offense” concept to the jury, emphasized the notion that the offense took place when appellants left the jail on August 26.50 Thus this is not a case where the jury was considering whether a defendant had escaped by failing to return. Appellants were tried and convicted of escaping by leaving the jail on August 26, and it was therefore error for the trial court to deny a choice of evils instruction on the ground that the defendants had not returned or adequately explained their continued absence. In effect, the trial court denied appellants’ right to have the jury consider a duress defense to the crime with which they had been charged (escaping on August 26) because the court found that they would in any event be guilty of an offense under a theory (failure to return)' that was never *1101presented either to appellants or to the jury. We cannot sanction such an obvious violation of appellants’ constitutional right to jury trial.
Under the circumstances of this case it is unnecessary for us to consider exhaustively the proper prerequisites to a choice of evils defense in escape cases.51 The trial court apparently gave this question considerable attention, and we do not know the nature of its prepared instruction except that were it not for the return requirement, which must be modified in accordance with our opinion,52 it was willing to have the jury consider the defense.53
C. Summary
We find prejudicial error in the District Court’s instruction on the element of “escape,” which prevented the jury from properly considering evidence relevant to appellants’ intent. The District Court also erred by imposing a return requirement as an absolute prerequisite to appellants’ proposed “duress” instruction, rather than instructing the jury that escape is a continuing offense and that such a defense must therefore justify a defendant’s continued absence as well as his initial departure. Appellants’ convictions must therefore be reversed and their cases remanded for a new trial.
II
Appellants also challenge the trial court's instructions and the sufficiency of the evidence with regard to another element of the offense: whether at the time they escaped they were in the custody of the Attorney General by virtue of the convictions alleged in the indictment.54 The indictment charged that all three appellants had been lawfully committed to the custody of the Attorney General by virtue of specific federal convictions and sentences and had escaped from such custody.55 The prosecution’s evidence indicated that Cooley was serving a sentence in the D.C. Jail, while Bailey and Walker, who were serving sentences in the federal facility in Leavenworth, Kansas, had been brought to the *1102D.C. Jail pursuant to writs of habeas corpus ad testificandum issued by the Superior Court for the District of Columbia.
Appellants raise two objections to the instructions and the evidence on the custody element of the offense. First, appellant Cooley argues that the prosecution’s evidence that he was in custody by virtue of his federal conviction at the time he escaped was insufficient as a matter of law. The prosecution relied primarily on documentary evidence to prove the custody element in all three cases.56 In Cooley’s case, for example, the Government introduced (1) a “face sheet” showing that Cooley was committed to the “D.C. Jail” on April 10, 1976 as a “federal prisoner” (Government Exhibit No. 8), (2) a Judgment and Commitment Order dated May 20, 1976 showing that following his conviction of Possession of an Unregistered Firearm, 26 U.S.C. § 5861(d) (1970), Cooley was sentenced and “committed to the custody of the Attorney General or his authorized representative for imprisonment for a period of five (5) years” (Government Exhibit No. 2), (3) an Escape and Apprehension Form dated August 26, 1976 noting that Cooley had escaped from the D.C. Jail on that date (Government Exhibit No. 5), and (4) the testimony of the Supervisor of Records at the D.C. Jail that there was no record of Cooley’s being released from the jail’s custody before August 26. Tr. at 27-28.
Since there was no specific documentary evidence, such as a return on the Judgment and Commitment Order, showing that the Attorney General committed him to the new D.C. Jail, Cooley argues that the evidence fails to prove that he was confined in the jail by virtue of the conviction alleged in the indictment. He draws support from Strickland v. United States, 339 F.2d 866 (10th Cir. 1965), a case in which the Tenth Circuit reversed a jury conviction under Section 751(a) because it held that evidence similar to that introduced here was insufficient as a matter of law to establish a prima facie case. Although the Government’s proof of a “chain of custody” pursuant to the convictions alleged in the indictment is not as strong as it could be, we do not agree that the prosecution’s evidence fails to establish a prima facie case as a matter of law.57 Reasonable inferences based on the evidence presented could enable a jury to find beyond a reasonable doubt that appellant Cooley was in custody by virtue of the convictions alleged in the indictment at the time he left confinement. Moreover, the trial court’s instructions with respect to Cooley’s custody were essentially correct.58
The second objection related to the custody element of the offense concerns only the appellants who were brought to the D.C. Jail pursuant to writs of habeas corpus ad testificandum— Bailey and Walker. The' trial court instructed the jury:
*1103Prisoners, such as two of the prisoners in this case, defendants in this case who are convicted in another jurisdiction and who were in the custody of the Attorney General, were brought to this jurisdiction as the documentary evidence shows, because they were summonsed [sic] as witnesses by another defendant in a proceeding then pending in the District of Columbia court. They are still under the custody today of the Attorney General regardless of how they happened to be brought into the District of Columbia Jail.
Tr. 800-801. Appellants claim that this instruction does not state the law and that it effectively removes an issue of fact from the jury’s consideration.
Appellants’ basic argument is that when a prisoner who has been committed to the custody of the Attorney General is transferred pursuant to a writ of habeas corpus ad testificandum, the prisoner is no longer in the custody of the Attorney General pursuant to the original commitment, but is in the custody of the court that issued the writ — -at least during the operation of the writ. Appellants therefore urge that, contrary to the instructions given by the trial court, there was a factual question whether they were in the custody of the Attorney General or of the Superior Court at the time they left the jail, and they claim further that the Government’s evidence on this factual issue was insufficient to establish a prima facie case.
Appellants claim to find authority for their position in the early Supreme Court
opinion in Barth v. Clise, 79 U.S. (12 Wall.) 400, 20 L.Ed. 393 (1870). That case was a suit against a sheriff to recover a debt owed to the plaintiff by a prisoner who had escaped while the sheriff was allegedly responsible for his safekeeping. The sheriff, who had arrested the prisoner pursuant to a writ of ne exeat obtained by the plaintiff, had brought the prisoner into court pursuant to a writ of habeas corpus obtained by the prisoner. The prisoner then escaped from the courtroom during the habeas corpus proceeding and fled to Canada. The Supreme Court held that the sheriff was not liable for the debt owed by the prisoner, explaining that once the sheriff had returned the prisoner to the court pursuant to the writ of habeas corpus, the responsibility for the safekeeping of the prisoner passed to the court “until the case is finally disposed of.” 79 U.S. (12 Wall.) at 402, 20 L.Ed. 393.
Citing broad language in Barth,59 appellants argue that unless the testimony for which they had been brought to the District, of Columbia had been completed, they were in custody pursuant to an order of the Superior Court and not by virtue of their federal convictions at the time they left the jail.60 Similar arguments based on Barth v. Clise have been raised in several previous escape cases brought under Section 751(a), but such arguments have never persuaded any court to find the requisite custody lacking in the case before it.61
Like these other cases, the case before us is distinguishable from Barth on several grounds. Barth dealt with the common law *1104liability of a custodian for the escape of a prisoner, while this case involves an interpretation of the terms of the federal escape statute. The prisoner in Barth escaped from the courtroom during the habeas proceeding, while appellants allegedly left an institution designated by the Attorney General for confinement of federal prisoners. Finally, Barth involved a writ of habeas corpus ad subjiciendum (the Great Writ), while the case before us concerns a writ of habeas corpus ad testificandum.
In light of these distinctions, we find that Barth does not prevent us from deciding that a prisoner who has been committed to the custody of the Attorney General by virtue of a conviction is still in the custody of the Attorney General by virtue of that conviction for the purposes of Section 751(a) when he is transferred pursuant to a writ of habeas corpus ad testificandum and confined in an institution designated by the Attorney General for the custody of federal prisoners. Policy considerations support at least this broad an interpretation of Section 751. The jurisdiction from which a prisoner is brought pursuant to a writ of habeas corpus has a significant interest in preventing the prisoner’s escape from custody. This interest has been recognized in an analogous situation by the drafters of the Interstate Agreement on Detainers (IAD), who provided that when a prisoner serving a sentence in one jurisdiction is brought to another jurisdiction for trial on another offense and escapes while in the receiving jurisdiction, he may be prosecuted under the escape statute of the sending jurisdiction.62
In addition to protecting the interest of the sending jurisdiction, holding that prisoners transferred by writs of habeas corpus ad testificandum are still in custody “by virtue of” the original commitment makes intuitive sense. The writ of habeas corpus ad testificandum is necessary only because the prisoner is already in custody elsewhere; the prisoner is kept confined when he is not testifying essentially because of the previous commitment; and any time during which the prisoner is confined under the writ counts toward satisfying the prisoner’s original sentence. Courts interpreting the term “custody” in escape cases63 and cases involving writs of habeas corpus 64 have demonstrated a flexibility responsive to such considerations of policy and common sense. Indeed, at least two other judicial decisions have in effect come to the same conclusion we reach.65
Although the trial judge’s instructions matched the general sense of our holding, we recognize that some portions of the instructions on this matter were confusing and might have invaded the province of the jury.66 We assume, however, that any such deficiencies in the instructions will be cured on remand.
*1105III
Appellants also raise other issues,67 but in light of our decision to grant a new trial on the ground of the erroneous instructions on “escape” we find it unnecessary to discuss these other questions.68 These cases are accordingly reversed and remanded to the District Court for further action consistent with this opinion.
Reversed and remanded.
. § 751. Prisoners in custody of institution or officer
(a) Whoever escapes or attempts to escape from the custody of the Attorney General or his authorized representative, or from any institution or facility in which he is confined by direction of the Attorney General, or from any custody under or by virtue of any process issued under the laws of the United States by any court, judge, or magistrate, or from the custody of an officer or employee of the United States pursuant to lawful arrest, shall, if the custody or confinement is by virtue of an arrest on a charge of felony, or conviction of any offense, be fined not more than $5,000 or imprisoned not more than five years, or both; or if the custody or confinement is for extradition or by virtue of an arrest or charge of or for a misdemeanor, and prior to conviction, be fined not more than $1,000 or imprisoned not more than one year, or both.
Appellants were also charged with violating 22 D.C.Code § 2601 (1973), the “local” statute defining the offense of “prison breach.” The jury was instructed that if they found the defendants guilty as charged under the federal escape statute, they should not consider the charge under the D.C.Code. Tr. 804.
. Courts issue writs of habeas corpus ad testifi-candum when it is necessary to bring a person who is confined in a prison or jail (usually serving a sentence for a previous conviction) into court to testify in a pending case. See generally Ex parte Bollman, 8 U.S. (4 Cranch) 75, 97, 2 L.Ed. 554 (1807) (Marshall, C. J.); 3 W. Blackstone, Commentaries * 129-131. Appellants were brought to the District to testify in a case pending before the Superior Court.
. For a brief discussion of the other issues, see note 68 infra.
. See, e. g., Tr. 150-152, 161-163, 168, 371, 377-378, 381, 390, 415, 547.
. See, e. g., Tr. 154, 368-370, 389-394, 411, 469-473.
. See, e. g., Tr. 368, 373-375, 404-405, 412, 475-478. Appellants Bailey and Walker were in the D. C. Jail pursuant to writs of habeas corpus ad testificandum so that they could testify in a criminal case in the Superior Court of the District of Columbia. Some of the alleged threats and abusive treatment were allegedly attempts by corrections officers to affect their testimony. As a result of this treatment appellant Bailey filed a suit in Superior Court against various guards, but the abusive treatment allegedly continued after the suit was filed. See, e. g., Tr. 529-533.
. See, e. g., Tr. 438 -158, 603-604, 625, 650-652, 678-680; appellant Walker’s Exhibit 2-A.
. See Tr. 404-405.
. Tr. 773. See text at note 22 infra. Any doubt the jurors may have had as to the relevance of appellants’ evidence to the issue of intent as defined by the trial court would have been resolved by the following instruction given by the court at the end of the case:
Now, ladies and gentlemen, the question has been raised during the course of this trial as to conditions at the District of Columbia Jail. I wish to say this to you with respect to that institution:
You are instructed as a matter of law that conditions at the District of Columbia Jail or the new detention center, no matter how burdensome or restrictive an individual inmate may find them to be, are not a defense to the charges in this case, nor justification for the commission of the offense of escape.
Tr. at 806. Furthermore, when the same judge later presided at the trial of a related case, he refused even to admit this type of evidence. See United States v. Cogdell, 190 U.S.App.D.C. -, - n.2, 585 F.2d 1130, 1132 n.2 (D.C. Cir. 1978).
. See text and note at note 43 infra.
. See United States v. Nix, 501 F.2d 516, 518 (7th Cir. 1974); W. LaFave & A. Scott, Handbook on Criminal Law 201-202 (1972).
The dissent characterizes the court’s opinion as a “bouleversement” that would create chaos in place of the alleged stability of traditional categories of criminal law — in large part because the court deals with the evidence at issue in this case under the rubric of “intent” as well as that of duress or necessity. The essential differences between the court and the dissent center around the proper roles of judge and jury, see note 28 infra, and are hardly so far-reaching as the dissent’s rhetoric suggests. Furthermore, the dissent exaggerates the stability of the law with regard to the defenses of duress and necessity. The rigid restrictions on the availability of these defenses upon which the dissent relies have been rejected by several modem statutes, including the Model Penal Code, and by several courts in escape cases. See, e. g., People v. Unger, 66 Ill.2d 333, 5 Ill.Dec. 848, 362 N.E.2d 319 (1977); People v. Luther, 394 Mich. 619, 232 N.W.2d 184 (1975); People v. Harmon, 53 Mich.App. 482, 220 N.W.2d 212 (1974); American Law Institute, Model Penal Code §§ 2.09 (Duress), 3.02 (Justification Generally: Choice of Evils) (Proposed Official Draft 1962); Hawaii Rev. Laws § 249-5 (1955); Ill.Rev.Stat, ch. 38, § 7-13 (1975). See also text and notes at notes 29-52 infra. The dissent’s accusation that the court is relying on “intent” because these other defenses are clearly unavailable on the facts of this case is thus without foundation.
. For example, the legal term “rape” is defined as “[t]he unlawful camal knowledge of a woman by a man forcibly and against her will.” Black’s Law Dictionary 1427 (4th ed. 1957). And the term “burglary” is defined as “[t]he breaking and entering the house of another in the nighttime, with intent to commit a felony therein, whether the felony be actually committed or not.” Id. at 247.
. United States v. Nix, supra note 11, 501 F.2d at 518-519, citing, inter alia, United States v. Snow, 157 U.S.App.D.C. 331, 484 F.2d 811 (1973); United States v. Chapman, 455 F.2d 746 (5th Cir. 1972); United States v. McPherson, 436 F.2d 1066 (5th Cir.), cert. denied, 402 U.S. 997, 91 S.Ct. 2181, 29 L.Ed.2d 163 (1971); Chandler v. United States, 378 F.2d 906 (9th Cir. 1967); Gallegos v. People, 159 Colo. 379, 411 P.2d 956 (1966); People v. Dolatowski, 94 Ill.App.2d 434, 237 N.E.2d 553 (1968); State v. Pace, 192 N.C. 780, 136 S.E. 11 (1926); State v. Hendrick, 164 N.W.2d 57 (N.D. 1969); State v. Lakin, 131 Vt. 82, 300 A.2d 554 (1973). See also Helton v. State, 311 So.2d 381 (Fla.App. 1975); Lewis v. State, 318 So.2d 529 (Fla.App. 1975), cert. denied, 334 So.2d 608 (Fla. 1976). Cases representing the minority view include People v. Siegel, 198 Cal.App.2d 676, 18 Cal. Rptr. 268 (1961); People v. Haskins, 177 Cal. App.2d 84, 2 Cal.Rptr. 34 (1960); State v. Wharff, 257 Iowa 871, 134 N.W.2d 922 (1965). Describing the requisite intent for escape as an “intent to leave and not to return” is not completely satisfactory since it might not cover a prisoner who intends to take an unauthorized temporary leave of absence. The Seventh Circuit’s own version of the intent requirement, “an intent to avoid confinement,” 501 F.2d at 519, captures the sense of these cases while avoiding the leave of absence loophole. See text and note at note 17 infra.
. United States v. Nix, supra note 11, 501 F.2d at 519, quoting Note, Criminal Attempts — The Rise and Fall of an Abstraction, 40 Yale L. J. 53, 69 (1930).
. See, e. g., United States v. Snow, supra note 13.
. This factor, though not explicitly stated in the Nix definition, was clearly implied. It is a generally recognized element of the definition of “escape” and was included in the trial court’s definition in this case when the jury was instructed that appellants’ departures must be “unauthorized.” See Tr. 802.
. The dissent fastens on the words “intent to avoid confinement” and would either reduce them to a statement of “general intent” indistinguishable from the “consciously and not inadvertently or by accident” instruction given by the trial court, or expand them to “intent to avoid confinement permanently.” See dissent, 190 U.S.App.D.C. at-, 585 F.2d at 1126-1127 (emphasis in original). Neither of these extreme interpretations is appropriate. The word “confinement” describes the most common form of punishment prescribed by our legal system. Jurors are readily aware that a person serving a sentence for a crime is “confined” — i. e., his liberty is restricted — in certain fundamental ways. For example, he cannot leave the institution wherein he is confined, he cannot come and go as he pleases, his daily schedule is subject to various controls, his privacy is substantially curtailed, and he is subject to strict discipline. One who leaves custody without permission to see his mother who is ill or to improve his menu (assuming the prison fare is within reason) has an intent to avoid confinement since restricted contact with relatives and a reasonably limited choice of diet are normal incidents of confinement. Furthermore, a prisoner who leaves custody to take even a temporary “leave of absence” from the normal conditions of confinement possesses the requisite intent for escape. On the other hand, if a prisoner offers evidence to show that he left confinement only to avoid conditions that are not normal aspects of “confinement” — such as beating in reprisal for testimony in a trial, failure to provide essential medical care, or homosexual attacks — the intent element of the crime of escape may not be satisfied. When a defendant introduces evidence that he was subject to such “non-confinement” conditions, the crucial factual determination on the intent issue is thus whether the defendant left custody only to avoid these conditions or whether, in addition, the defendant also intended to avoid confinement. In making this determination the jury is to be guided by the trial court’s instructions pointing out those factors that are most indicative of the presence or absence of an intent to avoid confinement. See text and notes at notes 20-21 infra.
Appellant Walker argues further that in order to violate § 751 a defendant must have the requisite intent at the time he leaves custody. Brief for appellant Walker at 40-43. He argues that § 751 should not be used to convict a prisoner who leaves with permission or without an intent to avoid confinement, noting that Congress has specifically provided a separate offense for one class of such prisoners — those on furlough who fail to return as prescribed. See 18 U.S.C. § 4082(c) (1976). Courts addressing this issue have not favored appellants’ position. See, e. g., United States v. Michelson, 559 F.2d 567, 570-571 (9th Cir. 1977); United States v. Spletzer, 535 F.2d 950 (5th Cir. 1976); United States v. Joiner, 496 F.2d 1314 (5th Cir.), cert. denied, 419 U.S. 1002, 95 S.Ct. 321, 42 L.Ed.2d 278 (1974); United States v. Woodring, 464 F.2d 1248, 1250 (10th Cir. 1972); United States v. Chapman, supra note 13, 455 F.2d at 749; Chandler v. United States, supra note 13, 378 F.2d at 908. We are sympathetic with the concern expressed in these cases that a prisoner should not be allowed to remain at large with impunity simply because his initial departure did not under the circumstances constitute a crime. We therefore agree that the trial court should instruct the jury that a prisoner who lacks the intent to avoid confinement at the time he leaves custody may nevertheless commit the crime of escape if he later forms this intent and therefore fails to report to the authorities or to turn himself in. See also text and note at note 43 infra.
. The jury must of course still apply the “beyond a reasonable doubt” standard to this inference. See In re Winship, 397 U.S. 358, 90 S.Ct. 1068, 25 L.Ed.2d 368 (1970).
. In order to be entitled to a special instruction on whether his intent to avoid confinement was negated by evidence of conditions in the jail, a defendant must, of course, introduce some evidence of these conditions. Since the evidence offered by appellants in this case was clearly “substantial,” we need not decide the minimum threshold of evidence necessary to entitle a defendant to this instruction. See generally United States v. Nix, supra note 11, 501 F.2d at 519-520; United States v. Grimes, 413 F.2d 1376 (7th Cir. 1969); Womack v. United States, 119 U.S.App.D.C. 40, 336 F.2d 959 (1964); Tatum v. United States, 88 U.S.App. D.C. 386, 391, 190 F.2d 612, 617 (1950).
. Such an instruction should also indicate the general boundaries between what is and is not “confinement.” See note 17 supra.
. Cf. United States v. Sheppard, 186 U.S.App. D.C. 283, 287, 569 F.2d 114, 118 (1977) (in a rape case, “[w]here the motivation of the complainant in bringing the charge is an issue, as in a case where the defendant contends that she consented to the intercourse, the defense attorney is free to emphasize to the jury the dangers of falsification, and the judge should instruct the jury as to those dangers and the difficulty of establishing consent”).
. The indictment in this case also alleged that appellants “did unlawfully and wilfully flee and escape” from custody. R. 32 (emphasis added).
. The dissent attempts to distinguish the Nix case by limiting that case to its facts and asserting that it holds only that intoxication may negate “general” as well as “specific” intent. Dissent, 190 U.S.App.D.C. at-, 585 F.2d at 1124-1125. This interpretation of the Nix opinion is untenable. Condemning the categorical rule that the relevance of such exculpatory factors as intoxication, coercion, and mistake depends on the mechanical and artificial classification of a crime as involving either specific or general intent, the Seventh Circuit rejected the specific/general intent terminology altogether and expressly refused to declare whether escape required “general” or “specific” intent. 501 F.2d at 518. Instead, the court followed a less categorical approach similar to that urged by some leading commentators, see W. LaFave & A. Scott, supra note 11, at 344: it focused on defining the intent element of the crime of escape and held (1) that a jury must be properly instructed as to this element, and (2) that if the defendant introduces adequate evidence of intoxication, the court should instruct the jury that it must consider whether the defendant was so intoxicated that he could not form the requisite intent. The Nix court did not limit its discussion to intoxication, but indicated its view that such factors as coercion and mistake could also negate the intent element of the crime of escape. See, e. g., 501 F.2d at 518 (“Whenever intoxication (or coercion or mistake) is raised as a mitigating factor, use of the ‘specific’ and ‘general’ intent labels interferes with the crucial analysis a court should make in escape cases: what constitutes the ‘escape’ element of the crime?”). We do no more than accept the Nix court’s holding that “escape” includes an “intent to avoid confinement” and outline how a court and jury should consider evidence of extreme conditions, unrelated to normal confinement, that is relevant to the existence of that intent. The procedures we adopt closely parallel those adopted by the court in Nix. See id. at 519-520. While the dissent seems willing enough to accept the “modem and ascendant view” with respect to intoxication in order to “distinguish” Nix, it is apparently unwilling to apply the basic principle underlying that “modem and ascendant view” to the facts of this case. Instead the dissent prefers to adhere to the mechanical specific/general intent terminology specifically rejected in Nix and to rely on such weak authority as the Woodring case, see text and note at note 22 supra, for the proposition that escape is a general intent crime. See dissent, 190 U.S.App.D.C. at-& n.84, 585 F.2d at 1124 & n.84.
. Some of the older cases would exclude such evidence altogether. See, e. g., People v. Whipple, 100 Cal.App. 261, 279 P. 1008 (1929). Other cases have treated such evidence as relevant to duress or necessity defenses and have imposed rigid limits on the availability of these defenses. See, e. g., People v. Lovercamp, 43 Cal.App.3d 823, 118 Cal.Rptr. 110 (1974); State v. Green, 470 S.W.2d 565 (Mo. 1971), cert. denied, 405 U.S. 1073, 92 S.Ct. 1491, 31 L.Ed.2d 806 (1972); Grubb v. State, 533 P.2d 988 (Okl.Cr.App. 1975); State v. Worley, 265 S.C. 551, 220 S.E.2d 242 (1975). See generally Annot., Duress, Necessity, or Conditions of Confinement as Justification for Escape from Prison, 69 A.L.R.3d 678 (1976). Courts adopting a more flexible approach include: People v. Unger, supra note 11; People v. Luther, supra note 11; People v. Harmon, supra note 11.
. See, e. g., United States v. Grayson, 550 F.2d 103 (3d Cir. 1977), cert. granted, 434 U.S. 816, 98 S.Ct. 53, 54 L.Ed.2d 71 (1977); United States v. Cluck, 542 F.2d 728 (8th Cir.), cert. denied, 429 U.S. 986, 97 S.Ct. 506, 50 L.Ed.2d 597 (1976); Syck v. State, 130 Ga.App. 50, 202 S.E.2d 464 (1973).
. See, e. g., State v. Green, supra note 24, 470 S.W.2d at 568 (Seiler, J., dissenting); People v. Whipple, supra note 24.
. See People v. Unger, supra note 11, 66 Ill.2d at 341, 5 Ill.Dec. at 852, 362 N.E.2d at 323. This court recently affirmed its confidence in the role of the jury as fact-finder in criminal cases in United States v. Sheppard, supra note 21. Sheppard discontinued the corroboration requirement in rape cases, relying on the adversary process and proper judicial instructions to guide the jury in reaching a just result. See note 21 supra.
. Despite the length of the dissent, its basic differences from the opinion of the court can be stated briefly. The fundamental theoretical difference is that the dissent refuses to accept the holding of the Nix court that an “escape” requires an “intent to avoid confinement.” See note 17 and text and notes at notes 11-14 supra. The dissent’s motive for rejecting the Nix holding is related to the basic practical differences between the two opinions: While the court and the dissent basically agree on what issues are relevant to weighing evidence of prison conditions in escape cases — e. g., the severity of conditions, the availability of alternatives to escape, the promptness and volun-tariness of return to custody — the dissent would hold all such evidence irrelevant as a matter of law unless it is determined that every one of five specific prerequisites related to these issues is met. The court, on the other hand, holds that, at least when a defendant, as in this case, introduces substantial evidence of extreme conditions, the jury is not absolutely prohibited from considering such evidence merely because certain inflexible prerequisites are not satisfied. In the court’s view, the factors represented by the prerequisites are the most significant considerations, but none of the prerequisites by itself is necessarily determinative. Once the defendant has presented a threshold amount of evidence, that evidence is to be considered by a properly instructed jury. See People v. Unger, supra note 11, 5 Ill.Dec. at 852, 362 N.E.2d at 323 (quoted in note 37 infra).
. Most of the arguments and evidence presented by appellants do not fit within the standard definition of a “duress” or “necessity” defense. The duress defense normally requires a defendant to establish that he engaged in criminal conduct only because he was compelled to do so by another person’s unlawful *1097threat which caused him reasonably to believe that he must commit the crime to avoid imminent death or serious bodily harm to himself or a third person. See W. LaFave & A. Scott, supra note 11, at 374-381. Only appellant Cooley’s claim that Walker and Bailey forced him to leave the jail fits this classic model comfortably. The standard necessity defense is available when “[t]he pressure of natural physical forces * * * confronts a person in an emergency with a choice of two evils” and when choosing the lesser of the two evils requires the person to violate the criminal law. Id. at 381, 382-388. Since appellants’ evidence involves human threats and forces, rather than natural physical ones, it does not establish a classic necessity defense. Courts and commentators have recognized the difficulties created, particularly in prison escape cases, by exculpatory evidence falling in between the traditional duress and necessity defenses and have proposed various solutions. See, e. g., United States v. Michelson, supra note 17; People v. Lovercamp, supra note 24; People v. Unger, supra note 11; People v. Luther, supra note 11; People v. Harmon, supra note 11; Gardner, The Defense of Necessity and the Right to Escape from Prison, 49 So.Cal.L.Rev. 110 (1975); Comment, Escape: The Defense of Duress and Necessity, 6 San Fran.L.Rev. 430 (1972); Note, Duress and the Prison Escape: A New Use for an Old Defense, 45 So.Cal.L.Rev. 1062 (1972); Casenote, People v. Harmon, 53 Mich.App. 482, 220 N.W.2d 212 (1974), 43 U.Cin.L.Rev. 956 (1974); Annot., supra note 24.
. See Model Penal Code § 2.09 (Proposed Official Draft 1962) and Commentary on § 2.09 (Tent.Draft No. 10 1960).
. The Model Penal Code includes the defense based on this principle, along with the defenses of intoxication and mistake, in Article 2: General Principles of Liability. The Model Penal Code defense based on the choice of evils principle, on the other hand, is included in Article 3: General Principles of Justification.
The dissent claims that every version of the duress defense must also satisfy the principle of “social utility” embodied in the “choice of evils” defense. Dissent at note 92. However, if, as the dissent suggests, duress can be a defense only where the harm to be avoided by committing an offense outweighs the harm caused by committing the offense, then any separate provision for a duress defense in a code that already contains a general choice-of-evils-type defense would be mere surplusage. Yet, as indicated above, the Model Penal Code contains both a general choice of evils defense and a duress defense.
. Appellants requested the following instruction on “duress”:
A defendant is not criminally responsible for the commission of the crime of willingly and voluntarily escaping from jail if he committed the act of escaping from incarceration as a result of coercion exerted on him.
Coercion which would excuse the commission of a criminal act must result from:
1) Threathening [sic ] conduct sufficient to create in the mind of a reasonable person the fear of death or serious bodily harm;
2) The conduct in fact caused such fear of death or serious bodily harm in the mind of the defendant;
3) The fear or duress was operating upon the mind of the defendant at the time of the alleged act; and
4) The defendant committed the act to avoid the threathened [sic] harm.
When evidence of coercion or duress is present, the Government must prove beyond a reasonable doubt that the defendant did not act under coercion. In other words, if you have a reasonable doubt whether or not the defendant acted under coercion as the court has defined it to you, your verdict must be not guilty.
R. 32A. This instruction might be interpreted as raising only the type of defense that would be covered under the instructions on intent set out above. On the other hand, given the theoretical confusion over the labels of duress and necessity and the principles underlying these defenses, appellants’ proposed instruction might also be construed to raise a choice of evils defense. We therefore consider that type of defense as well.
. See, e. g., Ill.Rev.Stat, ch. 38, § 7-13 (1975); Model Penal Code § 3.02 (Proposed Official Draft 1962) and Commentary on § 3.02 at 5 (Tent.Draft No. 8 1958); W. LaFave & A. Scott, supra note 11, at 378-379, 381-383. Even statements of the general principle vary in such aspects as the degree of objectivity required. The Model Penal Code, for example, requires that the balance of harms in fact favor commission of the crime, regardless of the defendant’s reasonable belief.
. W. LaFave & A. Scott, supra note 11, at 378.
. Id.
. See, e. g., cases cited in note 24 supra.
. The Model Penal Code provision reads: Section 3:02. Justification Generally: Choice of Evils.
(1) Conduct which the actor believes to be necessary to avoid a harm or evil to himself or to another is justifiable, provided that:
(a) the harm or evil sought to be avoided by such conduct is greater than that sought to be prevented by the law defining the offense charged; and
(b) neither the Code nor other law defining the offense provides exceptions or defenses dealing with the specific situation involved; and
(c) a legislative purpose to exclude the justification claimed does not otherwise plainly appear.
(2) When the actor was reckless or negligent in bringing about the situation requiring a choice of harms or evils or in appraising the necessity for his conduct, the justification afforded by this Section is unavailable in a prosecution for any offense for which recklessness or negligence, as the case may be, suffices to establish culpability.
Model Penal Code § 3.02 (Proposed Official Draft 1962). The Illinois Code section relied on by the court in People v. Unger, supra note 11, provides:
Conduct which would otherwise be an offense is justifiable by reason of necessity if the accused was without blame in occasioning or developing the situation and reasonably believed such conduct was necessary to avoid a public or private injury greater than the injury which might reasonably result from his own conduct.
Ill.Rev.Stat., ch. 38, § 7-13 (1975). The Unger court rejected an attempt to impose the rigid Lovercamp conditions in prison escape cases with the following comment:
We agree with the State and with the court in Lovercamp that the above conditions are relevant factors to be used in assessing claims of necessity. We cannot say, however, that the existence of each condition is, as a matter of law, necessary to establish a meritorious necessity defense.
The preconditions set forth in Lovercamp are, in our view, matters which go to the weight and credibility of the defendant’s testimony. The rule is well settled that a court will not weigh the evidence where the question is whether an instruction is justified. * * * The absence of one or more of the elements listed in Lovercamp would not necessarily mandate a finding that the defendant could not assert the defense of necessity.
362 N.E.2d at 323. See also People v. Luther, supra note 11; People v. Harmon, supra note 11.
. See note 32 supra.
. The dissent claims that appellants failed as a matter of law not only to satisfy the return requirement, but also to present sufficient evidence of the harm to be avoided to get to the jury. Dissent, 190 U.S.App.D.C. at-, 585 F.2d at 1116-1118. The dissent’s view on this point contradicts the opinion of the trial court, which was willing to submit a “duress” instruction except for appellants’ failure to meet the return requirement. See note 43 infra. In our view the trial court’s conclusion that the evidence on this point was sufficient to submit to the jury was clearly correct. The dissent’s narrow insistence on threats of “immediate” harm as an absolute prerequisite for the choice of evils defense seems particularly inappropriate in escape cases, where a possibility for escape (especially nonviolent escape) is not likely to remain available until a substantial threat becomes “immediate” in the narrow sense urged by the dissent.
. The “return requirement” has been described in various ways. In this case the trial court refused to allow appellants’ duress instruction because “[t]he defendants did not turn themselves in.” Tr. 807. Elsewhere in the proceedings the trial court suggested that “[h]ad these men notified the authorities or the public defender in an effort to surrender under conditions that might have been arranged by the public defender, then I would have permitted the duress and condition argument.” Tr. 778. People v. Lovercamp, supra note 24, establishes the return requirement in the following terms:
[A] limited defense of necessity is available if the following conditions exist: * * *
(5) The prisoner immediately reports to the proper authorities when he has attained a position of safety from the immediate threat. 118 Cal.Rptr. at 115.
. See note 32 supra for text of appellants’ proposed instruction.
. R. 35.
. The trial court expressly stated that if appellants had satisfied the return requirement, “I would have permitted the duress and condition argument. In fact, I have here an instruction, which I drew up very carefully with that in mind, but I realized that at the end of which I was calling upon the jury to make a finding that they couldn’t make, that is to say that these men had turned themselves in and that is a prerequisite to the assertion of the defense of duress, or coercion.” Tr. 778-779. Since the court’s instruction would have been given but for the return requirement, the choice of evils issue in this case turns on the validity of that requirement.
. The Lovercamp court’s version of the return requirement is quoted in note 40 supra. Since the prisoners in Lovercamp had been apprehended almost immediately after their departure, the appeals court remanded the case for a determination of whether appellants intended to surrender to the authorities.
. See also Stewart v. United States, 370 A.2d 1374 (D.C.Ct.App. 1977).
. The prisoner in Michelson allegedly feared that if he remained in prison he would be harmed by another inmate who had already injured him in a violent fight. 559 F.2d at 568.
. Michelson is also distinguishable from this case on the intent issue. The defense in that case did not raise the issue, and the court’s comments on the circumstances of the case indicate the reason for this: “The F.B.I. agent who arrested Michelson testified that Michelson, having been advised of his rights, freely admitted escaping * * * [and] also told the agent that his escape had been prompted not only by his beating by Santini, but also by the lengthy twenty-two year sentence imposed for the bank robbery and the Parole Board’s refusal to set a release date for him.” 559 F.2d at 568.
. We recognize the pressures that have led courts to construe escape as a continuing offense. See note 17 supra. Nevertheless, there is some force to appellants’ argument that this interpretation is not clear on the face of the statute, and the rule favoring strict construction of criminal statutes makes it important that the continuing offense concept be clearly explained to the jury.
. R. 32.
. For example, the trial court instructed the jury to consider whether the defendants had been convicted of a felony “at the time of the offense charged in the indictment, that is to say August 26th, 1976 * * Tr. 801. The trial court’s instructions when read as a whole clearly give the impression that appellants were being tried only for leaving the jail on August 26, and not for failing to return at some later date.
. See United States v. Michelson, supra note 17, 559 F.2d at 571 n.10.
. An acceptable version of the “return requirement” would include (1) an instruction that escape is a continuing offense, and (2) an instruction that a choice of evils defense cannot justify continued absence if the conditions establishing the defense (whatever the court determines them to be) do not continue for the period a prisoner remains at large.
. The dissent argues that the court “labor[s] mightily to exculpate these defendants.” Dissent, 190 U.S.App.D.C. at -, 585 F.2d at 1128. This statement wholly misconceives the issues in the court’s opinion. We do not even decide whether the conditions alleged by appellants actually existed, much less whether they justified appellants’ actions. Our concern is rather to clarify the law as to the relevance of appellants’ evidence and to assure that the jury is not denied the opportunity to perform its accustomed and constitutionally mandated functions. Indeed, it is the dissent that “labors mightily” to usurp the jury’s proper function when, for example, it rehearses its view of the evidence at length with the thinly veiled purpose of suggesting which witnesses are credible and which are not, dissent, 190 U.S.App.D.C. at -, 585 F.2d at 1106-1108, and when it complains that requiring the jury (and the defendants) to be adequately informed of the nature of the crime for which they are trying a defendant is “patently frivolous.” Dissent, 190 U.S.App.D.C. at-, 585 F.2d at 1116.
. The reason for a defendant’s confinement is important because of the penalty provisions of § 751(a), which vary the severity of the penalties depending on whether a defendant was in custody “by virtue of an arrest on a charge of felony, or conviction of any offense,” or “for extradition or by virtue of an arrest or charge of or for a misdemeanor, and prior to conviction * * 18 U.S.C. § 751(a) (for full text see note 1 supra).
. The charge against appellant Bailey is illustrative:
On or about August 26, 1976, within the District of Columbia, CLIFFORD BAILEY, having been lawfully committed to the custody of the Attorney General on March 6, 1973 and April 18, 1973, by virtue of a conviction and sentence imposed by the United States District Court for the District of Maryland in Criminal Case Numbers 72-0599 and 73-077, respectively, did unlawfully and wilfully flee and escape from such custody.
(Violation of Title 18, U.S.Code, Section 751(a))
R. 32.
. Appellants Bailey and Walker adopt appellant Cooley’s argument with respect to their own cases. Although the documentary evidence varied slightly among the three cases, the analysis of Cooley’s argument applies with equal force to the other two cases.
. The court in Strickland v. United States, 339 F.2d 866 (10th Cir. 1965), relied on Mullican v. United States, 252 F.2d 398 (5th Cir. 1958), a case in which certain documentary evidence linking a defendant’s custody when he escaped to the conviction alleged in his indictment was held inadmissible. Although the Mullican court found that the admission of the evidence had been prejudicial error, it did not dismiss the case (as the Strickland court did), but remanded for a new trial in which the jury would be allowed to decide the custody issue without the inadmissible evidence. 252 F.2d at 405.
. The trial court instructed the jury that in order to convict it must find beyond a reasonable doubt (1) that each appellant had been convicted of a felony, and (2) that “as a result of the conviction [each appellant] was committed to the custody of the Attorney General or [his] designated representative, and was in custody at the time of the offense.” Tr. 801-802. These instructions raise no problem, and we think it unlikely that the jury was confused by the court’s earlier statement that “with respect to each of the defendants who is on trial in this case the Court instructs you that defendants convicted either in this federal court or in the Superior Court of felonies, or in the federal court[s] throughout the country are committed to the custody of the Attorney General of the United States. This is a general practice and the Court will take judicial notice of it and instruct you accordingly.” Tr. 800.
. By the common law, upon the return of a writ of habeas corpus and the production of the body of the party suing it out, the authority under which the original commitment took place is superseded. After that time, and until the case is finally disposed of, the safe-keeping of the prisoner is entirely under the control and direction of the court to which the return is made. The prisoner is detained, not under the original commitment, but under the authority of the writ of habeas corpus. Pending the hearing he may be bailed de die in diem, or be remanded to the jail whence he came, or be committed to any other suitable place of confinement under the control of the court. * * *
Barth v. Clise, 79 U.S. (12 Wall.) 400, 402, 20 L.Ed. 393 (1879).
. The prosecution introduced no evidence at the trial as to whether appellants had completed their testimony in the Superior Court. Appellants Walker and Bailey therefore argue that their cases must be dismissed.
. See, e. g., United States v. Viger, 530 F.2d 846 (9th Cir. 1976); United States v. Stead, 528 F.2d 257 (8th Cir. 1975), cert. denied, 425 U.S. 953, 96 S.Ct. 1730, 48 L.Ed.2d 197 (1976); Tucker v. United States, 251 F.2d 794 (9th Cir. 1958).
. (g) For all purposes other than that for which temporary custody as provided in this agreement is exercised, the prisoner shall be deemed to remain in the custody of and subject to the jurisdiction of the sending State and any escape from temporary custody may be dealt with in the same manner as an escape from the original place of imprisonment or in any other manner permitted by law.
Interstate Agreement on Detainers, Article V(g), 18 U.S.C.App. (1976).
. See, e. g., United States v. Rudinsky, 439 F.2d 1074 (6th Cir. 1971) (prisoner on work release); Chandler v. United States, supra note 13, 378 F.2d at 908; Read v. United States, 361 F.2d 830 (10th Cir. 1966) (prisoner at recreation away from institution); Frazier v. United States, 119 U.S.App.D.C. 246, 339 F.2d 745 (1964) (prisoner in hospital outside institution).
. See, e. g., Hensley v. Municipal Court, 411 U.S. 345, 93 S.Ct. 1571, 36 L.Ed.2d 294 (1973); Peyton v. Rowe, 391 U.S. 54, 88 S.Ct. 1549, 20 L.Ed.2d 426 (1968); Jones v. Cunningham, 371 U.S. 236, 83 S.Ct. 373, 9 L.Ed.2d 285 (1963).
. United States v. Viger, supra note 61; Tucker v. United States, supra note 61. See also United States v. Hall, 451 F.2d 347 (4th Cir. 1971).
. An example is the court’s instruction that prisoners such as appellants Bailey and Walker “are still under the custody today of the Attorney General regardless of how they happened to be brought into the District of Columbia Jail.” Tr. 800-801.
. Despite its length, the dissent addresses only one of the issues raised by appellants. As the court’s opinion indicates, appellants raise several other substantial issues, some of which were unnecessary for the court to reach because the case is being reversed and remanded on the issue the dissent does address. Since the dissent would affirm rather than reverse, it would apparently decide all these other issues against appellants, but the dissent’s failure to concur in part or even to mention any of the other issues in these cases is curious.
. Some comments on a few of these other issues may be useful. Appellants Bailey and Walker seek to have their cases severed from that of appellant Cooley because of alleged prejudice from inconsistent and conflicting defenses (Bailey and Walker assert that they were forced to leave by conditions in the jail, while Cooley claims that, in addition to conditions in the jail, Bailey and Walker forced him to leave). The trial court denied a pretrial motion to sever based on prejudicial joinder under Rule 14, Fed.R.Crim.P., and refused to change its ruling after the evidence had been presented. For the first time on appeal appellants raise the further argument that joinder of all three cases in the indictment was improper under Rule 8(b), Fed.R.Crim.P. The Government responds that any Rule 8(b) objection was waived because it was not raised before trial. It claims that the Rule 14 motion made before trial cannot serve as a substitute for a Rule 8(b) objection. On remand appellants will be given a chance to raise their Rule 8(b) objection in timely fashion, and the trial court will have the benefit of knowing the precise nature of the alleged inconsistency of defenses if and when it again considers the issue of prejudicial joinder.
Appellant Bailey also argues that he was prejudiced by the introduction of evidence of a prior conviction of escape. This conviction was one for which he was allegedly in custody when he escaped, but Bailey claims that the prosecution could have relied solely on another conviction — of robbery — for which he was also allegedly in custody, and thus could have avoided the prejudicial impact of the prior escape conviction. Since the statute requires that the escapee must have been in custody by virtue of a conviction, evidence of any conviction for which a defendant is in custody when he escapes is directly relevant as long as this element is disputed. In the case on which appellant Bailey relies, United States v. Splet-zer, supra note 17, the defendant had stipulated to the conviction and confinement elements of the offense. This course is also open to appellant Bailey on remand.