Cite as: 514 U. S. 419 (1995)
Opinion of the Court
government fails or chooses not to disclose evidence that might prove helpful to the defense. 473 U. S., at 675, and n. 7. We have never held that the Constitution demands an open file policy (however such a policy might work out in practice), and the rule in Bagley (and, hence, in Brady) requires less of the prosecution than the ABA Standards for Criminal Justice, which call generally for prosecutorial disclosures of any evidence tending to exculpate or mitigate. See ABA Standards for Criminal Justice, Prosecution Function and Defense Function 3-3.11(a) (3d ed. 1993) ("A prosecutor should not intentionally fail to make timely disclosure to the defense, at the earliest feasible opportunity, of the existence of all evidence or information which tends to negate the guilt of the accused or mitigate the offense charged or which would tend to reduce the punishment of the accused"); ABA Model Rule of Professional Conduct 3.8(d) (1984) ("The prosecutor in a criminal case shall . . . make timely disclosure to the defense of all evidence or information known to the prosecutor that tends to negate the guilt of the accused or mitigates the offense").
While the definition of Bagley materiality in terms of the cumulative effect of suppression must accordingly be seen as leaving the government with a degree of discretion, it must also be understood as imposing a corresponding burden. On the one side, showing that the prosecution knew of an item of favorable evidence unknown to the defense does not amount to a Brady violation, without more. 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
437
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