Smith v. Cain, ___ U.S. ___, 132 S.Ct. 627 (Jan. 10, 2012) (prosecutor's failure to disclose contradictory statements of the sole eyewitness, whose testimony formed the basis of defendant's conviction, was a Brady violation requiring reversal of the conviction, because the statements are material where there is a reasonable probability that, had the evidence been disclosed, the result of the proceeding would have been different).