delivered the opinion of the Court.
The decision herein passes only on the integrity of a criminal trial in the federal courts. It does not determine the guilt or innocence of the petitioners, and we do not reach other issues propounded in the lengthy briefs or which may be present in the trial record of 5,147 pages. The Solicitor General of the United States moved to remand the case to the trial court for further proceedings because of untruthful testimony given before other tribunals by Joseph D. Mazzei, a Government witness in this case. The counter-motion of petitioners asked for a new trial. The decision is based entirely upon the representations of the Government in its written motion and on the statements of the Solicitor General during the argument on the motions.1
The petitioners were charged in a one-count indictment in the District Court for the Western District of Pennsylvania with conspiracy to violate the Smith Act.2 They *4were convicted, and the Court of Appeals for the Third Circuit, sitting en banc, affirmed by a divided court. 223 F. 2d 449. This Court granted the petition for writ of certiorari, 350 U. S. 922, and the case was scheduled for argument on October 10,1956.
On September 27, 1956, the Solicitor General of the United States filed a motion calling the attention of the Court to the testimony given in other proceedings by Mazzei, who was one of the seven witnesses for the Government in this case. In his motion, he stated that the Government, on the information in its possession, now has serious reason to doubt the truthfulness of Mazzei’s testimony in those proceedings. While adhering to its position that “the testimony given by Mazzei at the trial [in this case] was entirely truthful and credible,” the motion stated that “these incidents, taken cumulatively, lead us to suggest that the issue of his truthfulness at the trial of these petitioners should now be determined by the District Court after a hearing.”
The material cited by the Government indicating the untruthfulness of Mazzei on occasions other than this trial can best be presented by setting forth verbatim the description of these incidents presented in the Motion of the Government to Remand:
“On June 18, 1953, Mazzei testified before the Senate Permanent Subcommittee on Investigations, in Washington, D. C., that, at a meeting of the Civil Rights Congress on December 4, 1952, one Louis *5Bortz told him that he, Bortz, had been ‘selected by the Communist Party to do a job in the liquidation of Senator Joseph McCarthy.’ Mazzei further testified that the said Bortz conducted Communist Party classes in Pittsburgh to familiarize Party members with the handling of firearms and to instruct them in the construction of bombs.
“On November 14, 1952, Mazzei pleaded guilty to charges of adultery and bastardy in a Pennsylvania state court. This fact was brought out during his cross-examination at the petitioners’ trial. On October 2, 1953 — after the completion of the trial— Mazzei filed a petition in the state court to have the guilty plea set aside. One of the grounds set forth in his petition was that he ‘was not guilty of the charge to which he was induced to plead * * * but did so only in his official capacity (as a Government informant) at the insistence of his superior in the FBI to avoid testifying.’ At a hearing on the above petition on October 6, 1953, a Special Agent of the FBI denied Mazzei’s allegations under oath. Maz-zei’s petition was dismissed by the court on October 6, 1953.
“In November 1953, Mazzei, at a secret proceeding, identified a certain Government official as a long-time active Communist Party member.
“On June 10 and 11, 1955, Mazzei testified before the Senate Subcommittee on Internal Security regarding possible Communist influences motivating attempts to discredit Justice Michael Musmanno of the Supreme Court of Pennsylvania. In the course of his testimony, Mazzei identified John J. Mullen, National Director, Political Action Committee, Steel Workers of America, as a member of the Communist Party in Pittsburgh during the period that Mazzei *6was a Government informant. Mazzei also testified that since 1942 he met Mullen ten or fifteen times a year, as a fellow Communist Party member.
“On July 2, 1956, Mazzei testified in disbarment proceedings against one Leo Sheiner before the Circuit Court of the Eleventh Judicial Circuit of Florida, in Miami. On cross-examination, Mazzei reiterated his charge that he was induced to plead guilty to the adultery and bastardy charge in the Pennsylvania state court in November 1952 by an Agent of the FBI. Items of his testimony as to alleged Communist activity are as follows: — that he visited Dade County, Florida, on behalf of the Communist Party during each of the years from 1946 to 1952; that the Communist Party in Miami had attempted to lease a bus line which served the Opa-locka Air Base; that in 1948 the Communist Party made plans for the armed invasion of the United States on orders from the Soviet Union and that he, Mazzei, was selected to go to Miami in 1948 because it was a seaport; that he took courses in the Communist Party on sabotage, espionage, and handling arms and ammunition; that he was taught by officers of the Communist Party in Pittsburgh how to blow bridges, poison water in reservoirs, and to eliminate people; that he discussed with Sheiner in 1948 ‘knocking off’ a Judge Holt (a Florida judge) whom they (presumably the Communist Party) were having trouble with, and importing one Louis Bortz, the strong-arm man for the Communist Party, to do the job; that he and the Communist Party had made plans to assassinate Senators, Congressmen, and even went to Washington and beat up a Senator; and that, to his knowledge, Sheiner was extensively engaged in Communist Party activities in 1945, 1947, 1950, 1951, and 1952. *7None of this testimony at the Florida proceeding is supported or corroborated by information in the possession of the Government.
“Mazzei likewise testified that the FBI arranged to get him into the Army so that he could watch a certain Communist Party member; that he never wore a uniform and that he was discharged the day after the Communist Party member he was to watch was discharged. In actual fact, Mazzei’s career in the Army was the result of the operation of the Selective Training and Service Act of 1940 and the FBI had nothing to do with his service in the armed forces. He also testified that sometimes the FBI paid him about $1,000 a month for expenses. From the period 1942 to 1952, according to the Bureau records, Mazzei was paid the total of $172.05 as expense money.
“Mazzei likewise testified that he had never been arrested in his life. In fact, he was arrested in connection with the paternity case brought against him in Pennsylvania by one Irene Corva. He has been arrested several times subsequent to this for his failure to make support payments to this woman.”
On the argument of the motion the Solicitor General, in response to questions by the Court, stated with commendable candor that he believed the testimony given by Mazzei on June 18, 1953, before the Senate Committee concerning “the liquidation of Senator Joseph McCarthy” was untrue. He likewise stated that he believed the testimony given by Mazzei on July 2, 1956, in the Circuit Court of Florida was untrue. And in addition to the Solicitor General’s personal opinion, the text of the motion itself shows that the Department of Justice is certain that some of Mazzei’s post-trial testimony was contrary to the facts. The Pennsylvania statement of *8October 2, 1953, concerning his conviction of adultery and bastardy was controverted under oath at that hearing by an agent of the FBI. Mazzei again asserted in the Florida proceeding that he was induced to plead guilty to the adultery charge by an agent of the FBI. In the Florida testimony, he said that the FBI sometimes paid him a thousand dollars a month for expenses, whereas the records of the Bureau showed he was paid a total of $172.05 as expense money. He also testified there that the FBI arranged to put him in the Army to spy on a Party member, whereas the FBI had nothing to do with his Army service; he had been inducted in accordance with the Selective Service Act. All these discrepancies are pointed out in the motion, as quoted above.
As to his bizarre testimony in the Florida proceeding-concerning sabotage, espionage, handling of arms and ammunition, and plots to assassinate Senators, Congressmen, and a state judge, the Government’s motion suggests that none of it is worthy of belief by stating therein: “None of this testimony at the Florida proceeding is supported or corroborated by information in the possession of the Government.”
At the oral argument, however, the Solicitor General stated that although he believed all of this testimony to be untrue, he was not prepared to say the witness Mazzei was guilty of perjury in giving the testimony; that his untrue statements might have been caused by a psychiatric condition, and that such condition might have arisen subsequent to the time of this trial. The Solicitor General, in the light of this position, asked to have the argument on the main case stricken from the calendar and the case remanded to the District Court for a full consideration of the credibility of the testimony of witness Mazzei. Commendable as the action of the Solicitor General was in promptly bringing the matter to our *9attention when it came to the attention of his office,3 we do not believe the disposition of the case suggested by him should be made.
Either this Court or the District Court should accept the statements of the Solicitor General as indicating the unreliability of this Government witness. The question of whether his untruthfulness in these other proceedings constituted perjury or was caused by a psychiatric condition can make no material difference here. Whichever explanation might be found to be correct in this regard, Mazzei’s credibility has been wholly discredited by the disclosures of the Solicitor General. No other conclusion is possible. The dignity of the United States Government will not permit the conviction of any person on tainted testimony. This conviction is tainted, and there can be no other just result than to accord petitioners a new trial.
It must be remembered that we are not dealing here with a motion for a new trial initiated by the defense, under Rule 33 of the Federal Rules of Criminal Procedure, presenting untruthful statements by a Government witness subsequent to the trial as newly discovered evidence affecting his credibility at the trial. Such an allegation by the defense ordinarily will not support a motion for a new trial, because new evidence which is “merely cumulative or impeaching” is not, according to the often-repeated statement of the courts, an adequate basis for the grant of a new trial.4
*10Here we have an entirely different situation. The witness Mazzei was a paid informer of the Government — he had been in its employ from 1942 to 1953 for the purpose of infiltrating the Communist Party and reporting the facts found. He testified in this case in that capacity, as a Government witness. It is the Government which now questions the credibility of its own witness because in other proceedings in the same field of activity he gave certain testimony — some parts of it positively established as untrue and other parts of it believed by the Solicitor General to be untrue. The Solicitor General conceded that without Mazzei’s testimony in this case the conviction of two of the petitioners cannot stand, but he argued that as to the other three Mazzei’s evidence may not have had a substantial effect. But the trial judge believed Mazzei’s testimony was material against them for, over objection, he admitted it against all the defendants. There were only seven witnesses. The testimony of Mazzei, at least, gave flesh-and-blood reality to the mass of Communist literature read to the jury to show advocacy of violence by the Communist Party.5 This being so, it cannot be deter*11mined conclusively by any court that his testimony was insignificant in the general case against the defendants. Thus it has tainted the trial as to all petitioners. As we said last Term in Communist Party v. Subversive Activities Control Board:
“When uncontested challenge is made that a finding of subversive design by petitioner was in part the product of three perjurious witnesses, it does not remove the taint for a reviewing court to find that there is ample innocent testimony to support the Board’s findings. If these witnesses in fact committed perjury in testifying in other cases on subject matter substantially like that of their testimony in the present proceedings, their testimony in this proceeding is inevitably discredited and the Board’s determination must duly take this fact into account.” 351 U. S. 115, 124.
There we remanded to the Subversive Activities Control Board for reconsideration of its original determination in *12the light of the record shorn of the tainted testimony. But there the Board, an administrative agency, was the original finder of fact. Here, on the other hand, in a criminal case, the original finder of fact was a jury. The district judge is not the proper agency to determine that there was sufficient evidence at the trial, other than that given by Mazzei, to sustain a conviction of any of the petitioners. Only the jury can determine what it would do on a different body of evidence, and the jury can no longer act in this case.6 For this reason, as well as that stated in the preceding paragraph, if on a remand the District Court should rule that the verdict against some of the petitioners could stand, we would be obliged, on a subsequent appeal, to reverse and, at that late date, direct that a new trial be granted.7 This case was insti*13tuted four and one-half years ago; petitioners have been proceeding in forma pauperis. The interests of justice could not be served by a remand that must prove futile.
It might be different if we could see in this case any factual issue upon which the District Court, on a remand, could make an unassailable finding that Mazzei’s other falsehoods were differentiated from his testimony herein. But it is not within the realm of reason to expect the district judge to determine, as the Government indicated it would ask him to do, that the witness Mazzei testified truthfully in this case in 1953 as an undercover informer concerning the activities of the Communist conspiracy, yet concurrently appeared in the same role in another tribunal and testified falsely — possibly because of a psychiatric condition — about a plan by different members of the Communist conspiracy to assassinate a United States Senator.8 That would be an unreasonable determination to make even though the judge might believe that Mazzei's bizarre testimony in 1956 concerning plans for the assassination of other officials, the destruction of bridges, training in sabotage and handling arms, and the poisoning of water in reservoirs, all to destroy the Government of the United States, was the product of a mental or emotional con*14dition that had developed only after the time of this trial.
Mazzei, by his testimony, has poisoned the water in this reservoir, and the reservoir cannot be cleansed without first draining it of all impurity. This is a federal criminal case, and this Court has supervisory jurisdiction over the proceedings of the federal courts.9 If it has any duty to perform in this regard, it is to see that the waters of justice are not polluted. Pollution having taken place here, the condition should be remedied at the earliest opportunity.
“The untainted administration of justice is certainly one of the most cherished aspects of our institutions. Its observance is one of our proudest boasts. This Court is charged with supervisory functions in relation to proceedings in the federal courts. See McNabb v. United States, 318 U. S. 332. Therefore, fastidious regard for the honor of the administration of justice requires the Court to make certain that the doing of justice be made so manifest that only irrational or perverse claims of its disregard can be asserted.” Communist Party v. Subversive Activities Control Board, 351 U. S. 115, 124.
The government of a strong and free nation does not need convictions based upon such testimony. It cannot afford to abide with them. The interests of justice call for a reversal of the judgments below with direction to grant the petitioners a new trial.
It is so ordered.
Mr. Justice Brennan took no part in the consideration or decision of this case.The Court directed that oral argument on the motions be heard at the time previously scheduled for the argument .on the merits. 352 U. S. 808. Mr. Justice Frankfurter, believing the motion should be granted without argument, filed a dissent.
After hearing argument on the motions, October 10, 1956, the Court recessed to consider the matter, following which its decision to order a new trial was announced from the bench. 352 U. S. 862. Argument on the merits, therefore, was not heard. Mr. Justice Frankfurter, Mr. Justice Burton, and Mr. Justice Harlan dissented from the denial of the Government’s motion to remand.
This opinion has been written to amplify the decision announced October 10, 1956. It should be noted that Mr. Justice Minton participated in the consideration and decision of the motions, voting in favor of the order of the Court. On October 15, 1956, prior to the writing of this opinion, he retired from the Court. Therefore he did not participate in the consideration of this opinion.
It was alleged that between 1945 and the date of the indictment the petitioners had conspired to advocate the overthrow of the Gov*4ernment of the United States by force and violence and to organize a society or group, the Communist Party, devoted to that purpose. The trial judge ruled that the organization charge was barred by the statute of limitations, but that evidence concerning the 1945 organization of the Communist Party, as well as earlier events, was admissible in determining whether petitioners had conspired to advocate violence.
The Solicitor General’s motion stated that his office came into possession of “the history of Mazzei’s post-trial testimony” less than ten days before the motion was filed. With one exception, the motion does not indicate when other units of the Department of Justice acquired their information of Mazzei’s conduct.
See, e. g., United States v. Johnson, 142 F. 2d 588, 592, cert. dismissed, 323 U. S. 806; United States v. Rutkin, 208 F. 2d 647, *10654; United States v. Frankfeld, 111 F. Supp. 919, 923, aff’d sub nom. Meyers v. United States, 207 F. 2d 413. But see United States v. On Lee, 201 F. 2d 722, 725-726 (dissenting opinion).
See also United States v. Johnson, 327 U. S. 106, 110-111, n. 4 and n. 5.
Although we have not examined the evidence in this case, in view of the disposition made, we deem it appropriate to consider herein the nature of Mazzei’s testimony, since petitioners’ counter-motion referred us to the appropriate pages of the transcript. The same pages had also been cited in the main briefs of both parties in summarizing the evidence.
Mazzei testified quite specifically about statements by defendants Careathers and Dolsen, made in classes each had taught at a Communist Party school he had attended in 1943 or in private conversations each had had with him at that time.
Careathers taught in his class, Mazzei testified, about the part *11the Negro people would play in bringing about a revolution. [Tr. 1940-1941.] Dolsen told his class, with Careathers present, that the only way a revolution could come about would be by violent overthrow of the government, with the Communist Party helping. [Tr. 1923.] Mazzei related other details of Dolsen’s teaching, and passages were read to the jury which he said Dolsen had read to the class from the History of the Communist Party of the Soviet Union. [Tr. 1922-1923, 1936-1938.]
Mazzei told how Dolsen and Careathers had each given him private instruction after class, because each was unsatisfied with his understanding of a lesson in Dolsen’s class. Mazzei related that each had told him in these separate private sessions that a revolution in this country could only come by armed violence, and that it would be with the help of the Communist Party and the Soviet Union. [Tr. 1940, 1943.] Mazzei also testified that Dolsen had told him, on an auto trip, that if a revolution came about, he would not hesitate to kill, as he had done in China, where he had worked with the Communist Party. [Tr. 1945.]
Cf. Gordon v. United States, 344 U. S. 414, 422-423.
The present situation is different from that in United States v. Flynn, 130 F. Supp. 412, reargument denied, 131 F. Supp. 742. There the defense moved for a new trial on the basis of an affidavit in which a witness recanted his testimony after the trial. The Government charged that the recantation, rather than the testimony it contradicted, was the lie. Hence there was a factual issue to be determined at the outset, unlike the present case, where there is no conflict between the trial testimony and the subsequent matter brought forward by the Government as bearing on credibility. This difference has been recognized by the courts as calling for the application of different tests in passing on a motion for new trial, even without the added distinction of this case that it is the Government which questions the witness’s credibility. See, e. g., United States v. Johnson, 142 F. 2d 588, 591-592, cert. dismissed, 323 U. S. 806; United States v. Hiss, 107 F. Supp. 128, 136, aff’d, 201 F. 2d 372. Therefore, we express no opinion as to the procedure followed by Judge Dimock in the Flynn case.
Cf. Remmer v. United States, 347 U. S. 227, 348 U. S. 904, 350 U. S. 377.
Because the situation raised by the Solicitor General’s motion is quite distinct from that of the ordinary defense motion for new trial, see pp. 9-11, supra, we would not consider ourselves bound on a *13review of the District Court’s ruling in this situation by the limitations expressed with reference to the defense motion in United States v. Johnson, 327 U. S. 106.
See also note 6, supra.
The trial of petitioners started February 24, 1953. Mazzei testified against petitioners on March 26, 27, and 30. It was on June 18 that he testified before the Senate Committee. On July 9, a motion for a mistrial was made on the basis of the prejudice alleged to be caused petitioners by the publicity given the June 18 testimony of Mazzei concerning the assassination of Senator McCarthy. Mistrial was denied. The jury found petitioners guilty on August 20. They were sentenced on August 25, on which date motions for new trial were denied.
Cf. McNabb v. United States, 318 U. S. 332, 340-341; Thiel v. Southern Pacific Co., 328 U. S. 217, 225.