In the United States v. Bagley case of 1984, the Supreme Court held that withholding evidence favorable to a defendant violated their right to due process, regardless of whether it was done in good faith or not. The court ruled that such violations could result in reversing a conviction if there is reasonable probability that had the evidence been disclosed, the outcome would have been different. In this case, Benjamin Rucker Bagley was convicted for selling illegal firearms and drugs after two government informants testified against him. However, he later discovered contracts between these informants and the government which were not disclosed during his trial; hence he appealed on grounds of prosecutorial misconduct for failure to disclose exculpatory material.

In the dissenting opinion for United States v. Bagley, Justice Blackmun argued that the majority's decision to remand the case back to lower courts was unnecessary and complicated matters by introducing a new standard of materiality. He contended that it should be enough if there is a reasonable probability that disclosure of evidence favorable to the defense would have affected the outcome of proceedings. The introduction of this new standard, he believed, could lead prosecutors to withhold exculpatory information due its perceived insignificance in their eyes - an action which could potentially violate defendants' rights under Brady v. Maryland (1963). Furthermore, he disagreed with placing responsibility on trial judges for determining whether withheld evidence might have changed jury verdicts as they are not privy to deliberations or reasoning behind decisions made by juries.