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

The U.S. Supreme Court reversed the conviction and death sentence in Petitioner Kyle’s case where the state knowingly failed to disclose evidence favorable to the accused before and during trial. The Court reasoned that because the net effect of the evidence withheld by the state “raises a reasonable probability that its disclosure would have produced a different result at trial”, the court ordered a new trial and offered the following language in support:  

“Under United States v. Bagley, 473 U. S. 667, four aspects of materiality for Brady purposes bear emphasis. First, favorable evidence is material, and constitutional error results from its suppression by the government, if there is a “reasonable probability” that, had the evidence been disclosed to the defense, the result of the proceeding would have been different. Thus, a showing of materiality does not require demonstration by a preponderance that disclosure of the suppressed evidence would have resulted ultimately in the defendant’s acquittal. 473 U. S., at 682, 685. 

But the prosecution, which alone can know what is undisclosed, must be assigned the consequent responsibility to gauge the likely net effect of all such evidence and make disclosure when the point of “reasonable probability” is reached. This in turn means that the individual prosecutor has a duty to learn of any favorable evidence known to the others acting on the government’s behalf in the case, including the police. But whether the prosecutor succeeds or fails in meeting this obligation (whether, that is, a failure to disclose is in good faith or bad faith or bad faith, see Brady, 373 U. S., at 87), the prosecution’s responsibility for failing to disclose known, favorable evidence rising to a material level of importance is inescapable.”