Held: The withheld evidence is not material under Brady. Pp. 9-14.

     (a) The Government does not contest petitioners' claim that the withheld evidence was "favorable to the defense." Petitioners and the Government, however, do contest the materiality of the undisclosed Brady information. Such "evidence is 'material' . . . when there is a reasonable probability that, had the evidence been disclosed, the result of the proceeding would have been different." Cone v. Bell, 556 U. S. 449, 469-470. "A 'reasonable probability' of a different result" is one in which the suppressed evidence " 'undermines confidence in the outcome of the trial.' " Kyles v. Whitley, 514 U. S. 419, 434. To make that determination, this Court "evaluate[s]" the withheld evidence "in the context of the entire record." United States v. Agurs, 427 U. S. 97, 112. Pp. 9-11.

     (b) Petitioners' main argument is that, had they known about the withheld evidence, they could have challenged the Government's basic group attack theory by raising an alternative theory, namely, that a single perpetrator (or two at most) had attacked Fuller. Considering the withheld evidence "in the context of the entire record," Agurs, supra, at 112, that evidence is too little, too weak, or too distant from the main evidentiary points to meet Brady's standards.