On August 29, 1968, at approximately two a.m., Robert Mitchell was shot and killed on the corner of 7th and N Streets, N.W. The appellant, Perry Lynch, was arrested on October 4, 1968, and was tried by jury, beginning on *1014April 28, 1971, in the United States District Court for the District of Columbia upon a two-count indictment charging first degree murder1 and carrying a dangerous weapon.2 After all the evidence had been presented, the court granted appellant’s motion for a judgment of acquittal on the first degree murder charge but denied the motion for acquittal on the lesser included offenses. The case was submitted to the jury, which returned a verdict of guilty of both second degree murder and the dangerous weapons offense. The court imposed concurrent sentences of from five to twenty years for murder and of one year for carrying a dangerous weapon.
On appeal the appellant raises nine issues,3 the most significant of which are, in our view, (1) whether appellant’s right to a speedy trial guaranteed by the Sixth Amendment to the United States Constitution was. abridged by the delay of approximately thirty-one months from arrest to trial; and (2) whether the district court erred in admitting in evidence at trial the preliminary hearing testimony of the only eyewitness who identified appellant, when this witness, although apparently still within the jurisdiction of the court, *1015failed to appear at the trial. We conclude that under the peculiar circumstances of this case appellant was not denied his constitutional right to a speedy trial. We agree, however, that the government should not have been permitted to introduce the preliminary hearing testimony of the absent witness because it did not adequately demonstrate that this critical witness was “unavailable” at the time of trial. Accordingly, we hold that the admission of the preliminary hearing testimony at trial was erroneous as a matter of federal evidentiary law. Appellant’s conviction is vacated and because of our decision on this issue, we find it unnecessary to consider the other issues raised on appeal.
I
We consider, first, appellant’s contention that the lengthy interval between his arrest and trial was an undue delay that deprived him of his constitutional right to a speedy trial. In assessing this contention we are guided by the decision of the United States Supreme Court in Barker v. Wingo, 407 U.S. 514, 92 S.Ct. 2182, 33 L.Ed.2d 701 (1972), which declared that speedy trial claims require courts to employ a sensitive balancing process in which “the conduct of both the prosecution and the defendant are weighed.” 407 U.S. at 530. The Court identified some of the factors that should be considered in this necessarily ad hoc determination: “Length of delay, the reason for the delay, the defendant’s assertion of his right, and prejudice to the defendant.” 407 U.S. at 530 (footnote omitted).
With these criteria in mind, we first identify the period of delay that is properly challenged in this case. Appellant contests the government’s failure to bring him to trial for a period of thirty-one and one-half months after the date of the offense. Because United States v. Marion, 404 U.S. 307, 92 S.Ct. 455, 30 L.Ed.2d 468 (1971), established that the speedy trial right does not inhere until there is “either a formal indictment or information or else the actual restraints imposed by arrest and holding to answer a criminal charge,” 404 U.S. at 320, we do not consider any delay occurring before appellant’s arrest on October 4, 1968. Accordingly, we focus attention on the period of approximately thirty-one months from the date of arrest to the time of trial, April 28, 1971.
A delay of this magnitude must be examined critically by anyone concerned with the rights of criminal defendants and the broader interest of society in the fair but prompt administration of justice. However, this observation does not lead ineluctably to the conclusion that appellant was deprived of his right to a speedy trial.4 Instead, this delay draws our attention to the attendant costs to society and to possible prejudice to appellant and thereby mandates our inquiry into all factors relevant to a determination whether the constitutional right to a speedy trial has been abridged.
The first factor that we consider is the reason for the delay. We observe that different periods of delay occurred for different reasons. Although the shooting took place on August 29, 1968, appellant was not arrested until about one month later, on October 4. On October 17, 1968, a preliminary hearing was held. Appellant’s arraignment on the indictment was held on November 15. Approximately one month later, appellant filed a motion for a mental examination to determine his competency to stand trial. This motion was granted and appellant was admitted to Saint Elizabeths Hospital for a period not to exceed sixty days. This initial period was twice extended by the court for suc*1016cessive thirty-day periods. Then, without any further order of the court, as far as the record on appeal discloses, appellant was detained at the hospital until mid-January 1970, some time after the hospital’s report was finally filed with the court. The government conceded that “[t]he only cause for this lengthy examination period was the heavy backlog at Saint Elizabeths at the time.” Brief for Plaintiff-Appellee at 7.
The hospital’s report indicated that appellant was competent to stand trial. On February 25, 1970, appellant objected to the findings of the report. A hearing was scheduled for March 9, 1970, but was continued until March 23 to permit the defense to gain access to the records of the hospital evaluation. On March 23, appellant moved for the appointment of an independent psychiatrist to examine him. The motion was granted, and on April 14, Dr. John Cavanaugh, an independent psychiatrist, was appointed. Dr. Cavanaugh filed his report on April 29, 1970. A hearing followed on June 10 and subsequently the court determined that appellant was competent.
On August 17, 1970, appellant filed a motion for release on personal recognizance, and after a hearing on August 25, he was admitted to the work-release program.
Subsequently, on November 5, 1970, appellant for the first time filed a motion' to dismiss the indictment because he had been denied a speedy trial. It is significant that this first expression of appellant’s desire to expedite the proceedings did not occur until the expiration of more than two years and two months after his arrest. The motion was heard near the end of January 1971, at which time the court heard testimony of a detective about the availability of witnesses and entertained argument presented by appellant to demonstrate prejudice. Apparently the motion was denied, and when the case was called for trial on March 24, 1971, appellant renewed his motion to dismiss for lack of a speedy trial. The court entertained the motion and appellant presented additional testimony and argument. In addition, the court agreed to appoint another independent psychiatrist to examine appellant under the influence of sodium amytal to determine whether he had amnesia. On April 22, 1971, a hearing was held and the renewed motion to dismiss was apparently denied. Finally, on April 28 the trial was commenced.
This detailed factual outline makes it clear that we are not here concerned with a “deliberate attempt to delay the trial in order to hamper the defense,” 407 U.S. at 531, which would, of course, “be weighted heavily against the government.” Id. Appellant does not suggest, nor could he demonstrate on the record before us, that the government intentionally delayed prosecution “to gain some tactical advantage over [appellant] or to harass [him].” United States v. Marion, 404 U.S. 307, 325, 92 S.Ct. 455, 466, 30 L.Ed.2d 468 (1971). See Pollard v. United States, 325 U.S. 354, 361, 77 S.Ct. 481, 1 L.Ed.2d 393 (1957). Indeed, the record is barren of any indication, beyond the mere fact of delay itself, that the prosecution has not attempted to bring this indictment promptly to trial. Although we do not find it necessary to ascribe with mathematical precision various portions of the delay to the government, or, alternatively, to the defendant,5 we conclude that, *1017excluding momentarily the lengthy period of hospital examination, a major portion of the remaining delay is attributable to procedures initiated by appellant to protect his rights and to develop his defenses. Viewed in this light, cumulative delay occasioned by appellant’s objections and motions, and by hearings thereon and psychiatric examinations does not present a strong case for relief, As this court has previously recognized:
in any Case, where a principal cause of postponement is the deliberate pace of the system of safeguards designd *1018to protect the accused, the courts have been exceedingly reluctant to find constitutional infirmity even in very long delays.
Blunt v. United States, 131 U.S.App.D.C. 306, 310, 404 F.2d 1283, 1287 (1968), cert. denied, 394 U.S. 909, 89 S.Ct. 1021, 22 L.Ed.2d 221 (1969) (footnote omitted).
See also United States v. Ewell, 383 U.S. 116, 120, 86 S.Ct. 773, 15 L.Ed.2d 627 (1966); Wilkins v. United States, 129 U.S.App.D.C. 397, 395 F.2d 620 (1968); Hedgepeth v. United States, 124 U.S.App.D.C. 291, 364 F.2d 684 (1966).
We do not suggest that lengthy periods of time devoted substantially to procedures initiated by a defendant to protect his rights may never form the predicate for a determination that a speedy trial has been denied. But at least where this activity has not been further protracted by dilatory tactics engaged in by the prosecution, we are reluctant to assign controlling weight to delay occasioned by the defendant for his own protection.
There is, however, one segment of the delay here that cannot fairly be assigned to the appellant. In moving for a mental examination, the appellant cannot reasonably be held to have anticipated that an examination would require more than a year’s detention at Saint Elizabeths Hospital before the filing of a report on his competency to stand trial. Appellant in his brief accepts responsibility for the delay caused by commitment for the first sixty days at Saint Elizabeths Hospital. However, there remains a period of more than ten months of additional delay in Saint Elizabeths, in relation to which the only justification offered by the government was a “heavy backlog” at the hospital. Brief for Plaintiff-Appellee at 7. In Barker, the Supreme Court expressly noted that a “neutral reason such as negligence or overcrowded courts should be weighed less heavily [than an intentional attempt to delay trial to hamper the defense] but nevertheless should be considered since the ultimate responsibility for such circumstances must rest with the government rather than with the defendant.” 407 U.S. at 531. We neet not decide today whether Barker would require us to charge against the government undue delay occasioned by commitment for a hospital examination,6 for even assuming that ten months of the year-long detention in the hospital in this case should be charged against the government and assigned appropriate weight, this factor would not be controlling where, as here, appellant failed to assert his right to a speedy trial during this detention and also failed to show that he was prejudiced by this delay.
Here, appellant did not expressly assert his desire for a speedy trial until approximately two years and two months after his arrest. Moreover, appellant has not directed our attention to any other expression of his desire to expedite the proceedings before or during the lengthy detention at Saint Elizabeths Hospital for mental examination. To be sure, the Supreme Court in Bar-*1019her expressly rejected the rule that “a defendant waives any consideration of his right to a speedy trial for any period prior to which he has not demanded a trial.” 407 U.S. at 525. At the same time, however, the Court stressed that the defendant’s failure to assert his right is a factor entitled to “strong evidentiary weight in determining whether the defendant is being deprived of the right.” 407 U.S. at 532. The Court explained that the more serious the prejudice felt by the defendant, the more likely he is to complain. 407 U.S. at 531. Here, appellant’s failure to assert his right to a speedy trial for over two years, casts doubt on any claim that he was seriously prejudiced by the delays before his release from the hospital.
This observation leads us to a consideration of the fourth factor noted by the Supreme Court in Barker, prejudice to the defendant. The Court in Barker explained that “prejudice should be assessed in the light of the interests of defendants which the speedy trial right was designed to protect,” 407 U.S. at 532, and mentioned three such interests identified in its prior decisions: (1) the prevention of oppressive pretrial incarceration; (2) the minimization of anxiety and concern of the accused; and (3) the limitation of prejudice to the accused’s ability to defend. 407 U.S. at 532.
Appellant was incarcerated for approximately twenty-two months, including the detention in the hospital prior to his release under the work-release program. Ordinarily, such an extended pretrial, incarceration might be viewed as seriously prejudicial. But appellant’s failure to assert his rights weakens the suggestion that he suffered substantial personal prejudice in the form of either oppressive pretrial incarceration or anxiety and concern during that interval. There is no indication in the record that appellant was even treated any differently from other patients at the hospital. We hesitate to conclude that the detention of a drug addict like appellant in a hospital, where he is subject to positive influences and is the recipient of rehabilitative efforts is, without more, necessarily oppressive or productive of anxiety on his part, particularly where he has made no complaint.
In addition, whatever pretrial prejudice resulted from personal anxiety and restraint on appellant’s liberty after his November 5, 1970 motion to dismiss for lack of a speedy trial, during which time he was in the work-release program, does not appear substantial from anything that appellant has suggested.
Appellant relies primarily on cases decided by this court that suggest that when the delay in prosecution exceeds one year, prejudice is presumed and need not be affirmatively demonstrated. See, e. g., United States v. Holt, 145 U.S.App.D.C. 185, 448 F.2d 1108, cert. denied, 404 U.S. 942, 92 S.Ct. 292, 30 L.Ed.2d 257 (1969); Harling v. United States, 130 U.S.App.D.C. 327, 401 F.2d 392 (1968), cert. denied, 393 U.S. 1068, 89 S.Ct. 725, 21 L.Ed.2d 711 (1969); Hedgepeth v. United States, 124 U.S.App.D.C. 291, 364 F.2d 684 (1966). We need not at this time decide to what extent these precedents remain viable after Barker.7 It is sufficient to note that this court has previously declared that “even' the prejudice which is presumed to inhere in all cases where the delay is particularly long must be weighed against the other considerations .” United States v. Bishton, 150 U.S.App.D.C. 51, 463 F.2d 887, 891 (1972).
The Supreme Court in Barker indicated that the most serious form of prejudice is that which occurs when the de *1020fense is impaired by the delay; for example, where defense witnesses are “unable to recall accurately events of the distant past.” 407 U.S. at 532. Of course, the loss of memory by witnesses over long periods of time will ordinarily be less prejudicial to the defendant than to the prosecution, which bears the burden of proof at the trial.
Appellant argues that the amnesia, which he alleges developed after the crime and was caused in part by his incarceration, prejudiced his defense. However, we are not convinced that appellant’s defense was prejudiced materially by the delay for several reasons. In the first place, the record does not clearly demonstrate that appellant ever established the fact that he was actually suffering from amnesia. Indeed, implicit in the judicial determination that appellant was competent to stand trial is the finding that either no amnesia existed or, alternatively, that if amnesia existed it was not so severe as to preclude appellant from properly assisting in his own defense.8 Moreover, to the extent that any amnesia occurred prior to the delays, or from causes independent of delay, there is no justification for charging the resulting prejudice to the government. And apart from his assertion of amnesia affecting him, appellant does not claim his defense was impaired by the death, unavailability, or loss of memory of any other actual or potential witness.
Upon a careful consideration of all of the factors discussed above, we conclude that appellant was not denied his constitutional right to a speedy trial. Despite the long delay between arrest and trial, we decline to strike the balance against the governmnt under eircumstances where a major portion of the delay was caused by appellant’s own tactical maneuvering, where no intentionally dilatory practices can be ascribed to the government, where no demand for a speedy trial was made until most of the delay complained of had already occurred, and where only a tenuous demonstration of prejudice to appellant was shown. For these reasons we also reject appellant’s claim that reversal is required because of “unnecessary delay” under Rule 48(b) of the Federal Rules of Criminal Procedure.
II
We turn now to appellant’s contention that the district court erred in permitting the government in its case in chief to introduce into evidence the preliminary hearing testimony of Laverne Brown. Because Miss Brown’s status as a “crucial” government witness is significant, it is necessary to describe at some length the other evidence offered against appellant in connection with the death of Robert Mitchell.
There was substantial and undisputed evidence offered by the government at trial showing that the appellant was in close physical proximity to the deceased at the time of the fatal shooting. Shortly before the shooting, Mitchell, the deceased, who was a known seller of narcotics and an addict himself, was seen by several witnesses in the vicinity of 7th and N Streets. Priscilla Thompson testified that about ten or fifteen minutes prior to the shooting the deceased sold her some stockings in the carryout restaurant where she worked at the corner of 7th and N Streets. Decedent also attempted to sell some stockings to a woman in the company of Melvin Da*1021vis near the corner of 8th and N Streets before walking up toward the corner of 7th and N. About- five minutes later Davis observed appellant and a companion, James Wade, both known addicts, walking past him and proceeding in the direction of 7th Street. Five or ten minutes later, Davis heard several shots, and several minutes thereafter he saw a man running out of a nearby alley. Upon hearing a shot, Miss Thompson looked through the window in the carry-out shop and saw a man lying on the sidewalk. She then ran out into the street where she saw Wade taking money from the deceased’s pockets.
The testimony offered at trial by Wade himself portrayed a slightly different picture. Wade testified that he and appellant were walking together, that they saw Mitchell on the corner of 7th and N Streets, and that appellant said that he wanted to talk to Mitchell about something. Wade testified that he then walked off down 7th Street, but heard two shots before he had gone half a block. When he turned around, Wade testified he observed the deceased stagger and fall to the ground, and saw a person running although he could not identify who it was. Wade then approached Mitchell, bent over his body and “held his arm,” and then left the scene of the murder. Wade also testified that later that evening appellant came to his home to inject himself with drugs, and that appellant, in reference to the shooting, asked him “not to kick it around,” and stated that “the man grabbed the gun and it went off.”
Another witness, Ronald Crowder, who was walking with his girlfriend Laverne Brown and others to the carryout shop, testified that he saw Wade and another man, whom he could not identify, come down the street with a third man whom they had “against the wall.” Crowder also testified that he heard two shots, that he did not see the gun, but that Wade did not fire the shots.
Melvin Davis, Priscilla Thompson, and James Wade did not actually witness the shooting; and although Ronald Crowder saw the shooting, he could not identify the person who fired the shots.
Laverne Brown, who had been walking with Ronald Crowder, did not testify at trial, but because it was determined that she was “unavailable”, her testimony from appellant’s preliminary hearing was. read into evidence over the objection of the defense. This testimony reveals, and the government concedes, that Miss Brown was a “crucial” witness because she was the only eyewitness to the murder who identified appellant as the slayer. In contrast, the testimony of Davis and Thompson appears to implicate Wade as much as, if not more than, it implicates appellant.
Laverne Brown had testified at the preliminary hearing that she knew both Wade and appellant previously, and that she observed them walking together and approach a man who had been attempting to sell stockings. Appellant, she testified, asked the man “Do you have the stuff,” and after the man replied “no”, she heard appellant say something like “ ‘You’re going to get yours’ ”. Appellant and Wade then walked away but came back in about five minutes. Then, according to Miss Brown,. appellant shot the deceased while Wade stood a few feet away.
Although Miss Brown had appeared at pretrial proceedings and was seen in attendance at the trial, she failed to appear on May 3, 1971, the date on which the prosecution had intended to close its case with her testimony. Later that afternoon, the prosecutor explained to the court that although her family had been contacted, Miss Brown could not be located, and that he and a detective were unable to find Miss Brown at her residence. The trial was continued until the following morning. After presenting the testimony of another witness, the prosecutor declared that Miss Brown was still unavailable and sought to introduce her preliminary hearing testimony. After testimony about the prosecution’s efforts to locate Miss Brown and argument of counsel, the court ruled that Miss Brown was unavailable and that *1022her preliminary hearing testimony could be admitted and read into evidence.
Appellant contends that the admission of Miss Brown’s preliminary hearing testimony violated both the Sixth Amendment to the United States Constitution 9 and Rule 26 of the Federal Rules of Criminal Procedure.10 The first claim is derived from appellant’s constitutional right to be “confronted with witnesses against him.” The second claim is grounded upon the related common law evidentiary rule, applicable in the federal courts through Rule 26, that hearsay shall not be admitted unless it falls within a recognized exception.
Appellant supports both claims by his contention that Miss Brown was not “unavailable.” In addition, appellant bolsters his constitutional claim with the alternative theory that even if the witness were unavailable, the requirements of the confrontation clause were not met in this case because there was an inadequate opportunity for cross-examination at the preliminary hearing where appellant was represented by a different attorney. The government responds, first, that the evidence clearly established that Miss Brown was unavailable at the time of trial; and, second, that the requirements of the confrontation clause are clearly met where the defendant had an opportunity to cross-examine and did in fact cross-examine the witness at the preliminary hearing.
Preliminary hearing testimony is hearsay, McCormick on Evidence § 225, and hearsay evidence is generally inadmissible because it is less reliable than nonhearsay testimony: it may not have been offered under oath; there may have been no opportunity for cross-examination.; and the jury is given no opportunity to observe the demeanor of the witness. Id. § 224. However, under certain circumstances, exigencies permit the use of hearsay even in criminal trials, despite its dangers, and a number of exceptions to the general prohibition have been recognized by the courts.
In regard to the use of prior-recorded testimony in criminal trials offered for the truth of the matter in the statement, this court has declared:
It is the established rule in federal courts that testimony given in a former criminal trial is admissible in a retrial of that cause when the witness has become unavailable. The proponent of such evidence has the burden of establishing that the witness is unavailable ....
Coppedge v. United States, 114 U.S.App.D.C. 79, 311 F.2d 128, 132-133 (1962). See also McCormick on Evidence §§ 231, 234.
This rule finds support in the policies underlying the general prohibition of hearsay. And although the dangers of hearsay are mitigated to some extent by the safeguards of the oath and the opportunity to cross-examine in the former tribunal, the prior testimony should be admitted only when the witness is in fact “unavailable.” Certainly, it is preferable for a defendant to have the opportunity to cross-examine and impeach a witness at trial before the jury that will decide his guilt or innocence. The appearance of the witness will permit the jury to observe his demeanor and enable it to better assess his credibility. These considerations are especially cogent when the testimony of a witness is *1023critical to the prosecution’s case against the defendant.
The requirement that “unavailability” must be demonstrated as a predicate to the introduction of the pri- or-recorded testimony of a witness makes even more sense when, as here, it is prior testimony from a preliminary hearing, instead of that from a previous trial, which is sought to be introduced. In suitable cases there may be no constitutionally significant difference, for purposes of protecting confrontation rights, between the opportunity to cross-examine at a preliminary hearing and at a prior trial. California v. Green, 399 U.S. 149, 90 S.Ct. 1930, 26 L.Ed.2d 489 (1970). But a preliminary hearing is less likely to produce extensive cross-examination and impeachment of witnesses than a trial because of the different functions respectively of the trial, designed to determine guilt or innocence and the preliminary hearing, designed to determine only the existence vel non of probable cause to hold an accused to answer to the grand jury. See Barber v. Page, 390 U.S. 719, 725, 88 S.Ct. 1318, 20 L.Ed.2d 255 (1968). Therefore, it was incumbent upon the prosecution to demonstrate that Laverne Brown was unavailable as a necessary precondition to the introduction of her preliminary hearing testimony at appellant’s trial.
We conclude that the district court’s determination that Miss Brown was “unavailable” was erroneous. At least where the evidence indicates that a crucial government witness, who is physically and mentally capable of testifying, is within the jurisdiction of the court, the prosecution must demonstrate that it has been unable to obtain the witness’ presence through a search exercised both in good faith and with reasonable diligence and care. In the ordinary ease, this will require a search equally as vigorous as that which the government would undertake to find a critical witness if it has no preliminary hearing testimony to rely upon in the event of “unavailability.”
In attempting to prove that it met the requirements for unavailability, the prosecution made much of its efforts to locate Miss Brown. Miss Brown was personally served with a subpoena, and the prosecutor, who had observed Miss Brown in court during the trial, told her at the conclusion of the court day preceding the one on which her testimony was desired, to appear in court, ready to testify on Monday, May 3, 1971. When she failed to appear on Monday morning, the government called another witness and took steps to locate Miss Brown. After that witness testified, the trial was recessed early and the ease continued so the government .could continue its efforts to locate the missing witness. A detective was sent to locate Miss Brown. The detective went to the home of her grandmother, interrogated her about Miss Brown’s whereabouts, and ascertained that the grandmother thought she was across the street at an apartment with another girl. He then went to this apartment, knocked at the door and “kicked at the door to make sure whoever was in would have heard me.” He then went back to the grandmother’s house and asked one of Laverne’s younger brothers to try to arouse the occupants. He was unable to do so. The detective and his colleague then cruised the general area seeking to find her on the streets. That evening at 7 p. m., the detective again went to the home of the grandmother, who stated that she had not seen Miss Brown, but if she did she would call the homicide office to contact the detective. Subsequently, this detective left instructions for the detective who relieved him to have two men go to the grandmother’s house in the morning to attempt to locate the witness and “if she was not there, to cross the street [to the friend’s apártment].” These efforts did not result in any personal contact with Miss Brown. Subsequently, it was learned that Miss Brown was in the apartment when the detective first knocked, that she spent the night in the apartment, and left about 6 a. m. before the detec*1024fives arrived. The two detectives then stayed on the scene at the apartment and were still there waiting to locate the witness when the court convened.
Although appellant has not suggested, and we do not hold, that the prosecution acted in bad faith in attempting to locate Miss Brown, we conclude that the government’s efforts were insufficient. The prosecution does not claim to have inquired at the local hospitals, area police departments, the morgue, or of Miss Brown’s employer. Indeed, the government itself asserted that its efforts to locate Miss Brown were limited on May 3 because policemen were needed elsewhere to work on “disturbance matters” arising from the May Day peace demonstrations on the previous weekend and because many detectives were “sleeping after having worked 24 hours straight.”
Significantly, the prosecution represented in court on the morning of the 4th of May not only that Miss Brown had never expressed any unwillingness to testify but also that she was still in the jurisdiction. The prosecutor testified that Miss Brown had been in the apartment on the previous day and had refused to answer the door, that she had slept in the apartment overnight, and that the detectives had arrived at the apartment on the morning of May 4th too late to bring her to court because she had already departed at approximately 6. a. m. It is difficult to believe that if the preliminary hearing testimony of this critical witness were not available, the prosecution would have abandoned its efforts at this point to locate Miss Brown and concluded its case. We believe the prosecution would have asked the court for additional time within which to find her.
■ We are not prepared to equate “unavailability” with “evasiveness.” The government failed to establish that Miss Brown could not have been located and brought to trial by a reasonably diligent search. Accordingly, we hold that the witness was not “unavailable” and therefore the predicate for the introduction of Miss Brown’s preliminary hearing testimony at trial was not established. Moreover, the error was not harmless because the evidence improperly admitted was critical to the government’s case.
We recognize that the Supreme Court has observed that “merely because evidence is admitted in violation of a long-established hearsay rule does not lead to the automatic conclusion that confrontation rights have been denied.” California v. Green, supra, at 156. See also Dutton v. Evans, 400 U.S. 74, 80-83, 91 S.Ct. 210, 27 L.Ed.2d 213 (1970). However, because we base our holding solely on our supervisory powers and upon our view of the federal law of evidence,11 we do not need to decide whether appellant’s Sixth Amendment right of confrontation was violated by the admission of Miss Brown’s prior-recorded testimony.12
*1025Eeversed and remanded for a new trial.
. 22 D.C.Code § 2401 (1967).
. 22 D.C.Code § 3204 (1967).
. Appellant raises the following issues in his brief:
1. Whether the 31 month delay between arrest and trial, during which time the defendant is incarcerated, is a denial of the right to speedy trial when not more than three months of this delay is attributable to the defendant and when the major portion of the delay was caused by a one year incarceration at St. Elizabeths Hospital which was largely unjustified?
2. Whether, if prejudice other than mere incarceration is required to make out a case for denial of speedy trial, prejudice is found when it is shown that the defendant developed hysterical amnesia concerning the events of the crime and that the ability to cure this amnesia was proportionately reduced by the passage of time and because of the amnesia the defendant was denied the right to testify to facts [which were recalled under narco-analysis) would have exculpated him from criminal responsibility?
3. Whether the right to fair trial and effective assistance of counsel are violated when a defendant who is suffering from amnesia is deprived of the right to produce a valid and viable defense to the charge of first degree murder because he is unable to testify to facts which he recalled under narco-analysis and when the Government’s case does not foreclose all hypotheses of innocence?
4. Whether the right to confrontation and/or the Federal Rules of Criminal Procedure permit the use of, at a trial for first degree murder, the preliminary hearing transcript of the critical government witness who fails to appear for trial although still in the jurisdiction, when that preliminary hearing testimony is garbled and confused and when the defense counsel at the preliminary hearing had neither the time nor the tactical inclination to develop impeachment of the witness and when the rules of evidence at a preliminary hearing are such that full cross-examination is not permissible?
5. Whether a defendant in a first degree murder case who is unable to testify because he suffers from amnesia may be denied the right to explain his inability to testify in his own behalf to the jury by the use of expert medical testimony?
6. Whether a defendant who suffers from amnesia concerning the date of the crime may be denied his right to offer a defense to first degree murder when the only way that defense may be offered ' to the jury is through. the defendant’s statements made while under the influence of narco-analysis, when an extraordinarily qualified psychiatrist is of the opinion that the responses under narco-analysis were candid and accurate?
7. Whether an instruction on aiding and abetting is appropriate when there is no testimony that the defendant was anything but the principal?
8. Whether a witness who did not incriminate himself before the Grand Jury, though he testified, may be compelled to testify over objections at trial when his testimony at trial produces admissions of perjury before the Grand Jury and when that testimony is highly prejudicial to the defendant?
9. Whether it is proper to allow cross-examination beyond the scope of direct examination of a witness whose testimony in chief simply impeached the credibility of a Government witness, when the cross-examination elicits hearsay statements of others who did not testify which are highly prejudicial to the defendant?
. Indeed, in Barker v. Wingo, 407 U.S. 514, 92 S.Ct. 2182, 33 L.Ed.2d 101 (1972), the Supreme Court held that a delay of over five years between arrest and trial did not, under the circumstances presented in that case, deny the defendant his constitutional right to a speedy trial.
. On the basis of the following detailed analysis, the government asserts in its brief that the prosecution is not responsible for any significant delay in this case:
Thus from the time of appellant’s arrest on October 4, 1968 to the time of his trial April 28, 1971 there is an interval. of 30 months and 24 days, or roughly 31 months. Twelve months and one week (January 8, 1969-January 15, 1970) of this time were devoted to the mental examination of appellant at Saint Elizabeths, and the rendition of a competency report. Of the remaining 18 months, nearly 6 months (January 15-June 10) were devoted to disposition of appellant’s objections to the competency report, necessitating a hearing (March 9 and 23) and apparently *1017inspiring defense request for further examination by an independent psychiatrist (Dr. Cavanagh), all of which culminated in a competency determination. Consideration of appellant’s motion to dismiss the indictment, filed November 5, 1970 and renewed March 24 with the reception of considerable additional testimony ending with Dr. Yoehelson’s on April 22, involved a total of over five months (5 months and 23 days) before final disposition.
Thus over 11 of the approximate 30 months can be associated immediately with defense matters as time (excluding momentarily the period of hospital examination) devoted to hearings, psychiatric examinations, and disposition of appellant’s objections and motions. The approximate 20 months remaining include over 12 months for the Saint Elizabeths examination and report and a period of over 7 months between the apparent competency determination (June 10, 1970) and a status call of the case (January 10, 1971) when appellant’s pending speedy trial motion had to be scheduled for hearing.
It is immediately apparent to us that, while there is an unfortunately long interval before trial here, there is really little basis for attribution of any major portion of this time to the Government. It made no request for continuances, had no control over the case calendar system, and indeed tried to speedily bring this matter to trial. . . .
It would appear that if appellant believes he should claim the original 60 days for the hospital examination, it seems equally logical to assess against him the additional 60 days for that examination which Saint Elizabeths specifically requested since that time was apparently-made necessary by conditions beyond anyone’s control — surely the prosecution’s. For this reason, the entire examination period which ensued arguably should be assessed to him, or at least excluded from the computation of delay.
Moreover, clearly more than a month is involved for independent psychiatric examination, since appellant requested examination by Dr. Cavanagh (involving delay of the competency determination from March 23 to June 10, 1970, almost 3 months) as well as the examination by Dr. Yochelson which involved delay from March 24 to April 22, 1971 (almost a month). Thus, appellant’s own calculation of delay attributable to him should be nearer 8 months (4 months for hospital examination plus 4 months for private examinations) — or 16 months if the total hosjntal examination period is included.
The total period however for the disposition of his objections (January 15-June 10, 1970: 5 months, 5 days) and his motions (November 5, 1970-April 28, 1971: 5 months, 23 days) involving just these private examinations would be 10 months, 28 days, or approximately 11 months.
From the remaining 20 months, the entire hospital examination and reporting period of slightly over 12 months (January 8, 1969-January 15, 1970) should be excluded completely, if not assessed against appellant, leaving about 8 months.
Of these 8 months, almost 3 months (2 months, 26 days), representing the time between appellant’s arrest (October 4, 1968) and his commitment to Saint Elizabeths (January 8, 1969) must be excluded as time spent in preparation for trial.
The approximate 5 months remaining represent the period between appellant’s competency determination (June 10, 1970) and the filing of his speedy trial motion (November 5, 1970) during which there was virtually no significant activity in the case. Even that time is not taxable to the prosecution because during that intervening summer the prosecutor himself tried diligently to obtain a trial of this ease, even going to the unusual extent of asking another district judge to whom the case was not assigned to conduct the trial. It is apparent that the judge assigned this case became involved in a lengthy conspiracy case from sometime in September 1970 (shortly before appellant filed his speedy trial motion in November) until December 1970. Under the individual assignment system in the district court it was virtually impossible for this case to be tried at that time. In any event, it is at least clear that during this crucial period — the only significant time not covered by appellant’s examinations or pending claims — this case was “beyond the power of the prosecutor to expedite.” United States v. Bishton, [463 F.2d 887, 890 (D.C.Cir. 1972)].
Brief for Appellee at 9-12 (footnotes omitted).
. Undue delay resulting from overcrowded hospital facilities, like delay from overcrowded courts, might be charged against the government, by analogy to the principle stated in Barker. The prosecuting attorney does not control the hospital, of course, but neither is it in his power to prevent the delay occasioned by congested dockets and overcrowded courts. In both cases, the government, with its vast resources, is in a sense more responsible for the delay than the defendant. We observe, however, that there are some differences between the two cases. First, although no one would suggest that the defendant should not be permitted to request a mental examination, it may appear unfair to impose upon the government the burden for delay arising as a consequence of this procedure initiated by the defendant. In addition, there is presumably no shortage of attorneys who would accept positions as judges, but there may be a shortage of psychiatrists willing to work at St. Elizabeths and similar institutions across the country, and it can be argued, therefore, that delay caused by congestion in hospitals should not be charged aginst the government as readily as delay in the courts is. See Strunk v. United States, 412 U.S. 434, 93 S.Ct. 2260, 37 L.Ed.2d 56 (1973).
. In Barker the Supreme Court expressly left open the possibility of a “presumptive rule adopted by a court in the exercise of its supervisory power which establishes a fixed time period within which cases must normally be brought.” Barker v. Wingo, supra, at 530 n. 29. However, where a balancing test is undertaken in the absence of such a rule, the Barker decision appears to stress an evaluation and weighing of actual prejudice, rather than that which might merely be presumed.
. The provision governing mental competency, 18 U.S.C. § 4244 (1949), provides in relevant part:
Whenever after arrest and prior to the imposition of sentence or prior to the expiration of any period of probation the United States Attorney has reasonable cause to believe that a person charged with an offense against the United States may be presently insane or otherwise so mentally incompetent as to he unahle to understand the proceedings against him or properly to assist in his own, defense, he shall file a motion for a judicial determination of such mental competency of the accused, setting forth the ground for such belief with the trial court in which proceedings are pending. (Emphasis added.)
. The Sixth Amendment to the United States Constitution provides in relevant part:
In all criminal prosecutions, the accused shall enjoy the right . . . to be confronted with the witnesses against him
. Rule 26 of the Federal Rules of Criminal Procedure provides:
In all trials, the testimony of witnesses shall be taken orally in open court, unless otherwise provided by an act of Congress or by these rules. The admissibility of evidence . . . shall be governed . . . by the principles of the common law as they may be interpreted by the courts of the United States in the light of reason and experience.
. Id.
. In support of its argument for a relaxed standard of unavailability, the dissenting opinion cites Fed.R.Grim.P. 15(e). We regard this rule as inapposite for several reasons. It is elementary that legislation, or rules with the force and effect of legislation, may change common law standards for the admission of hearsay evidence so long as the confrontation clause of the Sixth Amendment, or any other relevant constitutional provision, is not offended. As the dissenting opinion recognizes, Rule 15 applies only to depositions taken by defendants. That rule has no application whatsoever here. We consider the admission of preliminary hearing testimony, not a deposition; and, in addition, the provisions of Rule 15 do not permit by their terms a deposition to be taken by the government. Moreover, even within the proper scope of its application, it is not clear that Rule 15(e) was intended to alter, as the dissenting opinion would, the common law test for unavailability. Rule 15(e) expressly provides for the use at trial of a deposition, meeting the provisions of the Rule, only “so far as otherwise admissible under the rules of evidence.” If these words are given their literal, meaning, then it begs the question to rely upon Rule 15(e) to support a watered-down standard for unavailability.
*1025Even if Buie 15(e) can be considered to have relaxed the standard of unavailability necessary for the admission of depositions noticed in accordance with its provisions, it does not suggest persuasively that by analogy a less rigorous prerequisite is good policy in other situations. Under Buie 15(a) a deposition may be taken in the first instance only in the limited circumstance where “it appears that a prospective witness may be unable to attend or prevented from attending a trial.” Accordingly, in every case where a deposition may subsequently be introduced at trial under Buie 15(e), the opposing party has previously had notice that the recorded testimony is likely to be offered at trial. So, advised, he can include in his cross-examination questions that will help a judge or jury make a credibility assessment of the deposed witness. If the diluted standard urged in the dissenting opinion were adopted, counsel, in an abundance of caution, would be encouraged to conduct his cross-examination at a preliminary hearing as extensively as he would at trial or, failing to do so, risk the charge of having rendered ineffective assistance to his client. This would unduly protract preliminary hearings and distort their proper function.
Despite the government’s concession that its efforts to locate Miss Brown were not up to par because of diminished police manpower following the crisis weekend of the May Day demonstrations, the dissenting opinion argues vigorously that what the government failed to do is wholly irrelevant because Miss Brown was in fact residing in her apartment. This fact, however, is not demonstrated in the record and the prosecution’s statement to that effect to the court was based on hearsay. Indeed, if she were engaged in fleeing the jurisdiction, a confederate could give her additional time by telling the police that she was still residing in her customary abode. Alternatively, if we accept as settled fact that she was still residing in her apartment and had not attempted to flee the jurisdiction, then with only minimal additional effort this critical witness could have been brought to trial to testify in person. To suggest that Miss Brown was unavailable in this case is to dilute, without precedent, the protection afforded criminal defendants by the common law. Considerations of prosecutorial convenience and expedience cannot justify this departure from established standards.
The dissenting opinion ignores the fact that in this case a man was convicted of murder on the basis of conflicting and largely circumstantial evidence, with the exception of Miss Brown’s preliminary hearing testimony, and that most of the testimony was elicited from persons who themselves were known to be addicts and a part of the same drug subculture in which both the deceased and the accused lived. If Miss Brown had altered her testimony at trial, or if the jury had declined to credit her testimony, the possibility that Wade, and not Lynch, had shot the deceased might have raised in the jurors’ minds a reasonable doubt about Lynch’s guilt. Although the dissenting opinion does not state that the admission of Miss Brown’s testimony was harmless to the defendant, nevertheless there is the recital that “[t]here is thus substantial additional evidence which demonstrates beyond a reasonable doubt that the ingredients of the offense were proved without the testimony of Laverne Brown.” Infra at 1036. We do not understand the evidence to support this assertion which might permit affirmance on the basis of harmless error.