Cite as: 527 U. S. 263 (1999)
Opinion of Souter, J.
mony, reversal was required if there was "any reasonable likelihood" that the false testimony had affected the verdict. Agurs, supra, at 103 (citing Giglio v. United States, 405 U. S. 150, 154 (1972), in turn quoting Napue v. Illinois, 360 U. S. 264, 271 (1959)). We have treated "reasonable likelihood" as synonymous with "reasonable possibility" and thus have equated materiality in the perjured-testimony cases with a showing that suppression of the evidence was not harmless beyond a reasonable doubt. Bagley, supra, at 678-680, and n. 9 (opinion of Blackmun, J.). See also Brecht v. Abraham-son, 507 U. S. 619, 637 (1993) (defining harmless-beyond-a-reasonable-doubt standard as no " 'reasonable possibility' that trial error contributed to the verdict"); Chapman v. California, 386 U. S. 18, 24 (1967) (same). In Agurs, we thought a less demanding standard appropriate when the prosecution fails to turn over materials in the absence of a specific request. Although we refrained from attaching a label to that standard, we explained it as falling between the more-likely-than-not level and yet another criterion, whether the reviewing court's " 'conviction [was] sure that the error did not influence the jury, or had but very slight effect.' " 427 U. S., at 112 (quoting Kotteakos v. United States, 328 U. S. 750, 764 (1946)). Finally, in United States v. Bagley, supra, we embraced "reasonable probability" as the appropriate standard to judge the materiality of information withheld by the prosecution whether or not the defense had asked first. Bagley took that phrase from Strickland v. Washington, 466 U. S. 668, 694 (1984), where it had been used for the level of prejudice needed to make out a claim of constitutionally ineffective assistance of counsel. Strickland in turn cited two cases for its formulation, Agurs (which did not contain the expression "reasonable probability") and United States v. Valenzuela-Bernal, 458 U. S. 858, 873-874 (1982) (which held that sanctions against the Government for deportation of a potential defense witness were appropriate only
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