delivered the opinion of the Court.
Respondent, a citizen of Mexico, was indicted in the United States District Court for the Southern District of California for transporting one Romero-Morales in violation of 8 U. S. C. § 1324(a)(2). That section generally prohibits the knowing transportation of an alien illegally in the United States who last entered the country within three years prior to the date of the transportation.1 Respondent was found guilty after a bench trial, but his conviction was overturned by the United States Court of Appeals for the Ninth Circuit. That court held that the action of the Government in deporting two aliens other than Romero-Morales violated respondent’s right under the Sixth Amendment to the United States Constitution to compulsory process, and his right under the Fifth Amendment to due process of law. We granted certiorari in order to review the Court of Appeals’ application of these constitutional provisions to this case, 454 U. S. 963 (1981),2 and we now reverse.
H-1
Respondent entered the United States illegally on March 23, 1980, and was taken by smugglers to a house in Escondido, Cal. Six days later, in exchange for his not having to pay the smugglers for bringing him across the border, respondent agreed to drive himself and five other passengers to Los Angeles. When the car which respondent was driving *861approached the Border Patrol checkpoint at Temecula, agents noticed the five passengers lying down inside the car and motioned to respondent to stop. Respondent accelerated through the checkpoint and was chased at high speed for approximately one mile before stopping the car and fleeing on foot along with the five passengers. Three of the passengers and respondent were apprehended by the Border Patrol agents.
Following their arrest, respondent and the other passengers were interviewed by criminal investigators. Respondent admitted his illegal entry into the country and explained his reason for not stopping at the checkpoint: “I was bringing the people [and] I already knew I had had it — too late — it was done.” App. 27. The three passengers also admitted that they were illegally in the country and each identified respondent as the driver of the car. Id., at 66. An Assistant United States Attorney concluded that the passengers possessed no evidence material to the prosecution or defense of respondent for transporting illegal aliens, and two of the passengers were deported to Mexico. The third, Enrique Romero-Morales, was detained to provide a nonhearsay basis for establishing that respondent had transported an illegal alien in violation of 8 U. S. C. § 1324(a)(2).
Respondent moved in the District Court to dismiss the indictment, claiming that the Government’s deportation of the two passengers other than Romero-Morales violated his Fifth Amendment right to due process of law and his Sixth Amendment right to compulsory process for obtaining favorable witnesses. He claimed that the deportation had deprived him of the opportunity to interview the two remaining passengers to determine whether they could aid in his defense. Although he had been in their presence throughout the allegedly criminal activity, respondent made no attempt to explain how the deported passengers could assist him in proving that he did not know that Romero-Morales was an illegal alien who had last entered the United States within the preceding three years.
*862At least one evidentiary hearing was held on respondent’s motion, at which Romero-Morales testified that he had not spoken to respondent during the entire time that they were together. At the same hearing the Government offered, without obtaining agreement by respondent, to stipulate that none of the passengers in the car told respondent that they were in the United States illegally. The District Court denied respondent’s motion and, following a bench trial on stipulated evidence, found respondent guilty as charged.3
The Court of Appeals reversed the conviction. The court relied upon the rule, first stated in United States v. Mendez-Rodriguez, 450 F. 2d 1 (CA9 1971), that the Government violates the Fifth and Sixth Amendments when it deports alien witnesses before defense counsel has an opportunity to interview them. 647 F. 2d 72, 73-75 (1981). Although it stated that a constitutional violation occurs only when “the alien’s testimony could conceivably benefit the defendant,” id., at 74, the court’s application of the “conceivable benefit” test demonstrated that the test will be satisfied whenever the deported aliens were eyewitnesses to the crime.4 Respond*863ent’s failure to explain what beneficial evidence would have been provided by the two passengers was thus inapposite, for “the deported aliens were eyewitnesses to, and active participants in, the crime charged, thus establishing a strong possibility that they could have provided material and relevant information concerning the events constituting the crime.” Id., at 75. Accordingly, the Court of Appeals held that respondent’s motion to dismiss the indictment should have been granted by the District Court.
i — I 1 — I
We think that the decision of the Court of Appeals in this case, and some of the additional arguments made in support of it by respondent, misapprehend the varied nature of the duties assigned to the Executive Branch by Congress. The Constitution imposes on the President the duty to “take Care that the Laws be faithfully executed.” U. S. Const., Art. II, § 3. One of the duties of the Executive Branch, and a vitally important one, is that of apprehending and obtaining the conviction of those who have violated criminal statutes of the United States. The prosecution of respondent is of course one example of the Executive’s effort to discharge that responsibility.
*864But the Government is charged with a dual responsibility when confronted with incidents such as that which resulted in the apprehension of respondent. One or more of the persons in the car may have violated the criminal laws enacted by Congress; but some or all of the persons in the car may also be subject to deportation as provided by Congress. The Government may, therefore, find itself confronted with the obligation of prosecuting persons in the position of respondent on criminal charges, and at the same time obligated to deport other persons involved in the event in order to carry out the immigration policies that Congress has enacted.
The power to regulate immigration — an attribute of sovereignty essential to the preservation of any nation — has been entrusted by the Constitution to the political branches of the Federal Government. See Mathews v. Diaz, 426 U. S. 67, 81 (1976). “The Court without exception has sustained Congress’ ‘plenary power to make rules for the admission of aliens.’” Kleindienst v. Mandel, 408 U. S. 758, 766 (1972) (quoting Boutilier v. INS, 387 U. S. 118, 123 (1967)). In exercising this power, Congress has adopted a policy of apprehending illegal aliens at or near the border and deporting them promptly. Border Patrol agents are authorized by statute to make warrantless arrests of aliens suspected of “attempting to enter the United States in violation of . . . law,” 8 U. S. C. § 1357(a)(2), and are directed to examine them without “unnecessary delay” to determine whether “there is prima facie evidence establishing” their attempted illegal entry. 8 CFR §287.3 (1982). Aliens against whom such evidence exists may be granted immediate voluntary departure from the country. See 8 U. S. C. § 1252(b); 8 CFR §242.5(a)(2)(i) (1982). Thus, Congress has determined that prompt deportation, such as occurred in this case, constitutes the most effective method for curbing the enormous flow of illegal aliens across our southern border.5
*865In addition to satisfying immigration policy, the prompt deportation of alien witnesses who are determined by the Government to possess no material evidence relevant to a criminal trial is justified by several practical considerations. During fiscal year 1979, almost one-half of the more than 11,000 inmates incarcerated in federal facilities in the Southern District of California were material witnesses who had neither been charged with nor convicted of a criminal offense. App. 18. The average period of detention for such witnesses exceeded 5 days, and many were detained for more than 20 days. Id., at 20. The resulting overcrowded conditions forced the Government to house many detainees in federal facilities located outside the Southern District of California or in state-operated jails. Id., at 21-22; Brief for United States 19. Thus, the detention of alien eyewitnesses imposes substantial financial and physical burdens upon the Government, not to mention the human cost to potential witnesses who are incarcerated though charged with no crime. In addition, the rule adopted by the Court of Appeals significantly constrains the Government’s prosecutorial discretion. As explained by the United States:
“Because of budget limitations and the unavailability of adequate detention facilities, it is simply impossible as a practical matter to prosecute many cases involving the transportation or harboring of large numbers of illegal aliens, where all the aliens must be incarcerated for a substantial period of time to avoid dismissal of the charges, even though the prosecution’s case may be overwhelming. As a consequence, many valid and appropriate prosecutions are foregone.” Id., at 21-22.
It simply will not do, therefore, to minimize the Government’s dilemma in cases like this with statements such as “[t]he prosecution may not deny access to a witness by hiding *866him out. See Freeman v. State of Georgia, 599 F. 2d 65 (5th Cir. 1979) (police detective concealed location of witness).” Brief for Respondent 35. Congress’ immigration policy and the practical considerations discussed above demonstrate that the Government had good reason to deport respondent’s passengers once it concluded that they possessed no evidence relevant to the prosecution or the defense of respondent’s criminal charge. No onus, in the sense of “hiding out” or “concealing” witnesses, attached to the Government by reason of its discharge of the obligations imposed upon it by Congress; its exercise of these manifold responsibilities is not to be judged by standards which might be appropriate if the Government’s only responsibility were to prosecute criminal offenses.
Ill
Viewing the Government’s conduct in this light, we turn to the evaluation of the Court of Appeals’ “conceivable benefit” test. There seems to us to be little doubt that this test is a virtual “per se” rule which requires little if any showing on the part of the accused defendant that the testimony of the absent witness would have been either favorable or material. As we said with respect to a similar test — phrased in terms of information “that might affect the jury’s verdict” — for determining when a prosecutor must disclose information to a criminal defendant:
“If everything that might influence a jury must be disclosed, the only way a prosecutor could discharge his constitutional duty would be to allow complete discovery of his files as a matter of routine practice.” United States v. Agurs, 427 U. S. 97, 109 (1976).
So it is with the “conceivable benefit” test. Given the vagaries of a typical jury trial, it would be a bold statement indeed to say that the testimony of any missing witness could not have “conceivably benefited” the defense. To us, the *867number of situations which will satisfy this test is limited only by the imaginations of judges or defense counsel.6
A
The only recent decision of this Court dealing with the right to compulsory process guaranteed by the Sixth Amendment suggests that more than the mere absence of testimony is necessary to establish a violation of the right. See Washington v. Texas, 388 U. S. 14 (1967). Indeed, the Sixth Amendment does not by its terms grant to a criminal defendant the right to secure the attendance and testimony of any and all witnesses: it guarantees him “compulsory process for obtaining witnesses in his favor.” U. S. Const., Arndt. 6 (emphasis added). In Washington, this Court found a violation of this Clause of the Sixth Amendment when the defendant was arbitrarily deprived of “testimony [that] would have been relevant and material, and . . . vital to the defense.” 388 U. S., at 16 (emphasis added). This language suggests that respondent cannot establish a violation of his constitutional right to compulsory process merely by showing that deportation of the passengers deprived him of their testimony. He must at least make some plausible showing of how their testimony would have been both material and favorable to his defense.7
When we turn from Washington to other cases in what might loosely be called the area of constitutionally guaranteed access to evidence, we find Washington's intimation of a *868materiality requirement more than borne out. Brady v. Maryland, 373 U. S. 83 (1963), held “that the suppression by the prosecution of evidence favorable to an accused upon request violates due process where the evidence is material either to guilt or to punishment, irrespective of the good faith or bad faith of the prosecution.” Id., at 87. This materiality requirement was emphasized in Moore v. Illinois, 408 U. S. 786 (1972), where we stated that a defendant will prevail upon a Brady claim “where the evidence is favorable to the accused and is material either to guilt or to punishment.” Id., at 794. And in United States v. Agurs, supra, we noted that “[a] fair analysis of the holding in Brady indicates that implicit in the requirement of materiality is a concern that the suppressed evidence might have affected the outcome of the trial.” Id., at 104. We further explained:
“The proper standard of materiality must reflect our overriding concern with the justice of the finding of guilt. . . . This means that the omission must be evaluated in the context of the entire record. If there is no reasonable doubt about guilt whether or not the additional evidence is considered, there is no justification for a new trial. On the other hand, if the verdict is already of questionable validity, additional evidence of relatively minor importance might be sufficient to create a reasonable doubt.” Id., at 112-113 (footnotes omitted).
Similarly, when the Government has been responsible for delay resulting in a loss of evidence to the accused, we have recognized a constitutional violation only when loss of the evidence prejudiced the defense. In United States v. Marion, 404 U. S. 307 (1971), for example, the Court held that preindictment delay claims were governed by the Due Process Clause of the Fifth Amendment, not by the speedy-trial guarantee of the Sixth Amendment. Elaborating on the nature of the guarantee provided by the Due Process Clause *869in such cases, the Court emphasized the requirement of materiality:
“Nor have appellees adequately demonstrated that the pre-indictment delay by the Government violated the Due Process Clause. No actual prejudice to the conduct of the defense is alleged or proved, and there is no showing that the Government intentionally delayed to gain some tactical advantage over appellees or to harass them.” Id., at 325.
Five Terms later, in United States v. Lovasco, 431 U. S. 783 (1977), we summarized this aspect of Marion:
“Thus Marion makes clear that proof of prejudice is generally a necessary but not sufficient element of a due process claim, and that the due process inquiry must consider the reasons for the delay as well as the prejudice to the accused.” Id., at 790.
The same “prejudice” requirement has been applied to cases of postindictment “delay. In Barker v. Wingo, 407 U. S. 514 (1972), the Court set forth several factors to be considered in determining whether an accused has been denied his Sixth Amendment right to a speedy trial by the Government’s pretrial delay. One of the four factors identified by the Court, and a factor more fully discussed in United States v. MacDonald, 435 U. S. 850, 858-859 (1978), was whether there had been any “prejudice to the defendant from the delay.” Id., at 858. Although the Court recognized that prejudice may take the form of “ ‘oppressive pretrial incarceration’” or “‘anxiety and concern of the accused,’” the “‘most serious’” consideration, analogous to considerations in this case, was impairment of the ability to mount a defense. See ibid, (quoting Barker v. Wingo, supra, at 532). Thus, other interests protected by the Sixth Amendment look to the degree of prejudice incurred by a defendant as a result of governmental action or inaction.
*870The principal difference between these cases in related areas of the law and the present case is that respondent simply had no access to the witnesses who were deported after he was criminally charged. Respondent contends that requiring him to show materiality is unreasonable in light of the fact that neither he nor his attorney was afforded an opportunity to interview the deported witnesses to determine what favorable information they possessed. But while this difference may well support a relaxation of the specificity required in showing materiality, we do not think that it affords the basis for wholly dispensing with such a showing.
The closest case in point is Roviaro v. United States, 353 U. S. 53 (1957). While Roviaro was not decided on the basis of constitutional claims, its subsequent affirmation in McCray v. Illinois, 386 U. S. 300 (1967), where both due process and confrontation claims were considered by the Court, suggests that Roviaro would not have been decided differently if those claims had actually been called to the Court’s attention.
Roviaro deals with the obligation of the prosecution to disclose to the defendant the name of an informer-eyewitness, and was cast in terms of the traditional governmental privilege to refuse disclosure of such an identity. The Roviaro Court held that the informer’s identity had to be disclosed, but only after it concluded that the informer’s testimony would be highly relevant:
“This is a case where the Government’s informer was the sole participant, other than the accused, in the transaction charged. The informer was the only witness in a position to amplify or contradict the testimony of government witnesses. Moreover, a government witness testified that [the informer] denied knowing petitioner or ever having seen him before. We conclude that, under these circumstances, the trial court committed prejudicial error in permitting the Government to withhold the identity of its undercover employee in the face of re*871peated demands by the accused for his disclosure.” 353 U. S., at 64-65.
“What Roviaro thus makes clear is that this Court was unwilling to impose any absolute rule requiring disclosure of an informer’s identity,” McCray v. Illinois, supra, at 311, despite the fact that criminal defendants otherwise have no access to such informers to determine what relevant information they possess. Roviaro supports the conclusion that while a defendant who has not had an opportunity to interview a witness may face a difficult task in making a showing of materiality, the task is not an impossible one. In such circumstances it is of course not possible to make any avowal of how a witness may testify. But the events to which a witness might testify, and the relevance of those events to the crime charged, may well demonstrate either the presence or absence of the required materiality.
In addition, it should be remembered that respondent was present throughout the commission of this crime. No one knows better than he what the deported witnesses actually said to him, or in his presence, that might bear upon whether he knew that Romero-Morales was an illegal alien who had entered the country within the past three years. And, in light of the actual charge made in the indictment, it was only the status of Romero-Morales which was relevant to the defense. Romero-Morales, of course, remained fully available for examination by the defendant and his attorney. We thus conclude that the respondent can establish no Sixth Amendment violation without making some plausible explanation of the assistance he would have received from the testimony of the deported witnesses.8
*872B
Having borrowed much of our reasoning with respect to the Compulsory Process Clause of the Sixth Amendment from cases involving the Due Process Clause of the Fifth Amendment, we have little difficulty holding that at least the same materiality requirement obtains with respect to a due process claim. Due process guarantees that a criminal defendant will be treated with “that fundamental fairness essential to the very concept of justice. In order to declare a denial of it we must find that the absence of that fairness fatally infected the trial; the acts complained of must be of such quality as necessarily prevents a fair trial.” Lisenba v. California, 314 U. S. 219, 236 (1941). In another setting, we recognized that Jencks Act violations, wherein the Government withholds evidence required by statute to be disclosed, rise to the level of due process violations only when they so infect the fairness of the trial as to make it “more a spectacle or trial by ordeal than a disciplined contest.” United States v. Augenblick, 393 U. S. 348, 356 (1969) (citations omitted). Such an absence of fairness is not made out by the Government’s deportation of the witnesses in this case unless there is some explanation of how their testimony would have been favorable and material. See United States v. Lovasco, 431 U. S. 783 (1977); United States v. Marion, 404 U. S. 307 (1971).
IV
To summarize, the responsibility of the Executive Branch faithfully to execute the immigration policy adopted by Congress justifies the prompt deportation of illegal-alien witnesses upon the Executive’s good-faith determination that they possess no evidence favorable to the defendant in a criminal prosecution. The mere fact that the Government *873deports such witnesses is not sufficient to establish a violation of the Compulsory Process Clause of the Sixth Amendment or the Due Process Clause of the Fifth Amendment. A violation of these provisions requires some showing that the evidence lost would be both material and favorable to the defense.
Because prompt deportation deprives the defendant of an opportunity to interview the witnesses to determine precisely what favorable evidence they possess, however, the defendant cannot be expected to render a detailed description of their lost testimony. But this does not, as the Court of Appeals concluded, relieve the defendant of the duty to make some showing of materiality. Sanctions may be imposed on the Government for deporting witnesses only if the criminal defendant makes a plausible showing that the testimony of the deported witnesses would have been material and favorable to his defense, in ways not merely cumulative to the testimony of available witnesses. In some cases such a showing may be based upon agreed facts, and will be in the nature of a legal argument rather than a submission of additional facts. In other cases the criminal defendant may advance additional facts, either consistent with facts already known to the court or accompanied by a reasonable explanation for their inconsistency with such facts, with a view to persuading the court that the testimony of a deported witness would have been material and favorable to his defense.9 Because in the latter situation the explanation of materiality is testimonial in nature, and constitutes evidence of the prejudice incurred as a result of the deportation, it should be verified by oath or affirmation of either the defendant or his attorney. See Fed. Rule Evid. 603; Fed. Rule Crim. Proc. 47.
As in other cases concerning the loss of material evidence, sanctions will be warranted for deportation of alien witnesses *874only if there is a reasonable likelihood that the testimony could have affected the judgment of the trier of fact. See Giglio v. United States, 405 U. S. 150, 154 (1972). In making such a determination, courts should afford some leeway for the fact that the defendant necessarily proffers a description of the material evidence rather than the evidence itself. Because determinations of materiality are often best made in light of all of the evidence adduced at trial, judges may wish to defer ruling on motions until after the presentation of evidence.10
In this case the respondent made no effort to explain what material, favorable evidence the deported passengers would have provided for his defense. Under the principles set forth today, he' therefore failed to establish a violation of the Fifth or Sixth Amendment, and the District Court did not err in denying his motion to dismiss the indictment. Accordingly, the judgment of the Court of Appeals is
Reversed.
Section 1324(a)(2) applies to “[a]ny person” who “transports, or moves, or attempts to transport or move,” “any alien,” “knowing that [the alien] is in the United States in violation of law, and knowing or having reasonable grounds to believe that his last entry into the United States occurred less than three years prior” to the transportation or attempted transportation with which the person is charged.
Other Courts of Appeals have adopted slight variations of the position held by the Court of Appeals for the Ninth Circuit. See, e. g., United States v. Armijo-Martinez, 669 F. 2d 1131 (CA6 1982); United States v. Rose, 669 F. 2d 23 (CA1 1982); United States v. Avila-Dominguez, 610 F. 2d 1266 (CA5 1980); United States v. Calzada, 579 F. 2d 1358 (CA7 1978).
The joint appendix contains excerpts of transcribed testimony from a hearing on June 2, 1980, at which the District Court heard arguments of counsel and the testimony of Romero-Morales. At the conclusion of this testimony, counsel for respondent proposed the highly unusual step of calling the Assistant United States Attorney as a witness. App. 45. The attorney testified at further proceedings held on June 12, 1980, and was interrogated, inter alia, about his understanding of various decisions of the Court of Appeals for the Ninth Circuit and about the Government’s litigating strategy in these cases. Id., at 63-64. This procedure seems to us highly unusual, if not bizarre; ordinarily the litigating strategies of the United States Attorney are no more the subject of permissible inquiry by his opponent than would be the litigating strategies of the Public Defender by his opponent.
As the Court of Appeals explained:
“The conceivable benefit in Mendez-Rodriguez stemmed from the fact that the deported aliens were eyewitnesses to, and active participants in, the crime charged, so that there was a strong possibility that they could have provided material and relevant evidence concerning the events constituting the crime. Conversely, where a missing deported alien was not an *863eyewitness to the offense, we have been unwilling to assume that the alien’s testimony could conceivably benefit the defendant.” 647 F. 2d, at 74 (citation and footnotes omitted).
As described by the Court of Appeals, the “conceivable benefit” test “impose[s] no requirement of government misconduct or negligence before dismissal of an indictment is warranted. Nor is a defendant required to show specific prejudice caused by the unavailability of the alien eyewitnesses.” Ibid, (citation omitted). Other Courts of Appeals have recognized the Ninth Circuit rule as requiring no showing of prejudice, United States v. Calzada, 579 F. 2d, at 1362, and as permitting dismissal of the indictment even when the “ ‘record is completely devoid of anything which would suggest that the testimony of any one, or more, of the deported persons would have been helpful’ to the defendants.” United States v. Avila-Dominguez, 610 F. 2d, at 1269-1270 (quoting United States v. Mendez-Rodriguez, 450 F. 2d 1, 6 (CA9 1971) (Kilkenny, J., dissenting)).
As evidence of the effectiveness of Congress’ policy and of the colossal problem presented by illegal entries from Mexico, the United States notes that approximately one million illegal aliens were detained by Border Pa*865trol officials during each of the three years preceding 1981. Brief for United States 19; see U. S. Department of Justice, Internal Audit Report, U. S. Border Patrol Management of the Mexican Border 1, 6 (Jan. 1981).
See n. 4, supra.
That the Sixth Amendment does not guarantee criminal defendants the right to compel the attendance of any and all witnesses is reflected in the Federal Rules of Criminal Procedure. Rule 17(b) requires the Government to subpoena witnesses on behalf of indigent defendants, but only “upon a satisfactory showing. . . that the presence of the witness is necessary to an adequate defense.” See also Isaacs v. United States, 159 U. S. 487, 489 (1895); Crumpton v. United States, 138 U. S. 361, 364-365 (1891).
Respondent’s knowledge of the truth distinguishes this ease from United States v. Burr, 25 F. Cas. 187 (No. 14,694) (CC Va. 1807), a ease cited by respondent in support of his argument that it is unreasonable to require him to explain the relevance of the missing testimony. In Burr, Chief Justice Marshall found it unreasonable to require Aaron Burr to explain the relevancy of General Wilkinson’s letter to President Jefferson, *872upon which the President’s allegations of treason were based, precisely because Burr had never read the letter and was unaware of its contents. In this case, respondent observed the passengers, heard their comments, and is fully aware of the ways in which they influenced his knowledge about the status of Romero-Morales.
In adopting this standard, we express no opinion on the showing which a criminal defendant must make in order to obtain compulsory process for securing the attendance at his criminal trial of witnesses within the United States.
The counsel of United States v. Agurs, 427 U. S. 97, 112-113 (1976), is helpful here:
“[T]he omission must be evaluated in the context of the entire record. If there is no reasonable doubt about guilt whether or not additional evidence is considered, there is no justification for a new trial. On the other hand, if the verdict is already of questionable validity, additional evidence of relatively minor importance might be sufficient to create a reasonable doubt.”