405 U.S. 150 (1972)
Petitioner John Giglio was convicted of passing forged money orders and sentenced to five years’ imprisonment.1 While his appeal was pending in the Court of Appeals, defense counsel discovered new evidence.2 This evidence indicated that the Government had failed to disclose an alleged promise made to its key witness that he would not be prosecuted if he testified for the Government.3
In June 1966, officials at the Manufacturers Hanover Trust Co. discovered that Robert Taliento, a teller at the bank, had cashed several forged money orders.4 Upon questioning by FBI agents, Taliento confessed to supplying Giglio with one of the bank’s customer signature cards used to forge $2,300 in money orders, which Taliento then processed through the regular channels of the bank.5 Taliento related this story to the grand jury, resulting in Giglio's indictment, after which Taliento was named as a coconspirator but not indicted.6
At trial, which commenced two years after indictment, Taliento testified identifying Giglio as the instigator of the scheme.7 Defense counsel cross-examined Taliento about possible agreements for prosecutorial leniency, and Taliento stated that nobody told him he would not be prosecuted and that he believed he still could be prosecuted.8 In summation, the Government attorney stated that Taliento received no promises that he would not be indicted.9
The issue arose on Giglio's motion for a new trial based on newly discovered evidence.10 An affidavit from Assistant United States Attorney DiPaola confirmed that he had promised Taliento that if he testified before the grand jury and at trial he would not be prosecuted.11 Assistant Golden, who handled the trial, filed an affidavit stating that DiPaola had assured him before trial that no promises of immunity had been made to Taliento.12 The United States Attorney Hoey filed an affidavit stating that he had personally consulted with Taliento and his attorney shortly before trial.13 He emphasized that Taliento would definitely be prosecuted if he did not testify.14 If he did testify he would be obliged to rely on the good judgment and conscience of the Government as to whether he would be prosecuted.15 The District Court did not resolve the apparent conflict between the two assistants. It proceeded on the theory that even if a promise had been made, it was not authorized and its disclosure would not have affected the verdict.16
Whether the evidence not disclosed was such as to require a new trial under the due process criteria of Napue v. Illinois and Brady v. Maryland?17
A new trial is required if the false testimony could in any reasonable likelihood have affected the judgment of the jury.18
Yes. When the reliability of a given witness may well be determinative of guilt or innocence, nondisclosure of evidence affecting credibility falls within this general rule.19 The established facts show that the Government's case depended almost entirely on Taliento's testimony. Without it there could have been no indictment and no evidence to carry the case to the jury.20
Taliento's credibility as a witness was therefore an important issue in the case. Evidence of any understanding or agreement as to a future prosecution would be relevant to his credibility and the jury was entitled to know of it.21
For these reasons, the due process requirements enunciated in Napue and the other cases cited earlier require a new trial, and the judgment of conviction is therefore reversed and the case is remanded for further proceedings consistent with this opinion.22