Giglio and Kyles: Witness Deals and the Full Disclosure Picture

Giglio v. United States, 405 U.S. 150 (1972)

Kyles v. Whitley, 514 U.S. 419 (1995)

Supreme Court of the United States · Witness credibility / disclosure

Giglio: promises to a key witness

An undisclosed promise of nonprosecution to a key witness can undermine the fairness of a trial. Evidence affecting credibility matters when the witness’s reliability may determine guilt or innocence. Giglio also treats the prosecutor’s office as an entity: one prosecutor’s promise cannot be disregarded simply because the trial prosecutor did not know about it.

Kyles: consider the evidence together

Materiality is assessed through the cumulative effect of suppressed favorable evidence, not by isolating each item. The prosecutor must learn of favorable evidence known to others acting for the government in the case, including police. The question is whether disclosure creates a reasonable probability of a different result—not whether acquittal was more likely than not.

Research questions

Were promises, inconsistent statements, or other credibility materials withheld? How do all suppressed items affect the case together?

Read the opinions

https://www.law.cornell.edu/supremecourt/text/405/150

https://www.law.cornell.edu/supremecourt/text/514/419

Educational information, not legal advice. Verify current law and procedural requirements with qualified counsel.