Giglio v. United States
The Court ruled that a man convicted of forging money orders deserves a new trial because the government's key witness had secretly been promised he would not be prosecuted, and that promise was never disclosed to the jury.
The decision holds that a promise made by any prosecutor in an office counts as a promise by the government as a whole, even if the prosecutor who tried the case didn't know about it — meaning offices must keep track of such deals and turn them over to the defense.
“A promise made by one attorney must be attributed, for these purposes, to the Government.”
The Court's rule that promises by any prosecutor bind the whole prosecutor's office.
How it got here: After conviction, while the appeal was pending, defense counsel discovered evidence of an undisclosed promise to the key witness and moved for a new trial, which the trial court denied.
The Case in Depth
What happened
A man was convicted of passing forged bank money orders based largely on the testimony of a bank teller who said the man had supplied a stolen signature card used to forge the orders. The teller, who could have been charged as a co-conspirator, was never indicted and testified against the man at trial, denying at trial that he had been promised he wouldn't be prosecuted.
The question before the Court
If a prosecutor's office promises a key witness he won't be charged, but the trial prosecutor doesn't know and denies it happened, does hiding that promise from the jury violate the defendant's rights?
Why it matters
Prosecutors' offices now bear responsibility for tracking every deal made with a witness, even across different attorneys handling the same case, and must disclose those deals to defendants. This protects defendants from convictions built on witness testimony whose credibility the jury never got to fully assess, and pushes offices to create internal systems for sharing such information.
What changes now
The conviction is reversed and the case goes back to the trial court for further proceedings, which will likely include a new trial at which the jury can hear evidence about the promise made to the witness and weigh his credibility accordingly. The ruling does not decide guilt or innocence — it only restores the defendant's chance to have a jury evaluate the full picture of the witness's incentives to testify.
What this does not decide
The Court did not decide whether the assistant prosecutor actually had authority to make the promise, or resolve the conflicting accounts between the two prosecutors about what was said. It also did not rule on the defendant's guilt, only that the jury should have heard about the undisclosed promise.
How the Court got there
The legal reasoning, step by step
- The Court applied the rule from Napue v. Illinois and Brady v. Maryland that the government violates due process — the constitutional guarantee of a fair trial — when it lets false or misleading testimony about a witness's credibility go uncorrected, regardless of whether the suppression was deliberate or accidental.
- A new trial is required only if the undisclosed evidence is material, meaning there is a reasonable likelihood it could have affected the jury's judgment, rather than every minor detail a defense lawyer might have found useful.
- The Court treated the prosecutor's office as a single institutional entity rather than a collection of individual lawyers, so a promise made by one assistant prosecutor is legally attributed to the government as a whole, even if the prosecutor who tried the case did not know about it.
- Because the witness's testimony was essentially the entire case against the defendant, his credibility was a central issue, and any undisclosed promise affecting his motive to testify favorably for the government was relevant and should have reached the jury.
- Applying this materiality standard, the Court concluded the undisclosed promise could reasonably have affected the jury's verdict, so the due process violation required a new trial.
Doctrinal impact
Cases affected by this decision
Reaffirms Napue v. Illinois (360 U. S. 264)
Reaffirmed that letting false or misleading witness testimony go uncorrected violates due process.
Reaffirms Brady v. Maryland (373 U. S. 83)
Reaffirmed that suppressing material evidence requires a new trial regardless of prosecutor's good or bad faith.
Reaffirms Mooney v. Holohan (294 U. S. 103)
Reaffirmed that knowingly using false evidence against a defendant violates basic fairness.
Reaffirms Pyle v. Kansas (317 U. S. 213)
Reaffirmed as part of the line of cases barring deliberate deception of courts and juries.