We now hold that the suppression by the prosecution of evidence favorable to an accused upon request violates due process where the evidence is material either to guilt or to punishment, irrespective of the good faith or bad faith of the prosecution.
The principle of Mooney v. Holohan is not punishment of society for misdeeds of a prosecutor, but avoidance of an unfair trial to the accused. Society wins not only when the guilty are convicted, but when criminal trials are fair; our system of the administration of justice suffers when any accused is treated unfairly. An inscription on the walls of the Department of Justice states the proposition candidly for the federal domain: "The United States wins its point whenever justice is done its citizens in the courts." A prosecution that withholds evidence on demand of an accused which, if made available, would tend to exculpate him or reduce the penalty helps shape a trial that bears heavily on the defendant. That casts the prosecutor in the role of an architect of a proceeding that does not comport with standards of justice, even though, as in the present case, his action is not "the result of guile," to use the words of the Court of Appeals. 226 Md. at 427, 174 A.2d at 169.
Brady v. Maryland, 373 U.S. 83 (1963)