For a defendant to successfully claim a Brady violation, three essential elements must be present:
Suppression by the Prosecution
The first element requires that the prosecution either intentionally or inadvertently withhold evidence. This suppression can occur in various ways, such as failing to disclose a police report, witness statements, forensic evidence, or other materials that could be advantageous to the defense. The duty to disclose applies not only to the prosecution team but also to law enforcement agencies working on the case.
Favorable to the Defense
The suppressed evidence must be favorable to the defendant, meaning that it could help exonerate the defendant, reduce the severity of the charges, or diminish the credibility of the prosecution's witnesses. Favorable evidence can be either exculpatory, directly pointing to the defendant's innocence, or impeachment evidence, which challenges the credibility of the prosecution's evidence or witnesses.
Materiality
The final element of a Brady violation is materiality. The suppressed evidence must be material to the case, meaning that there is a reasonable probability that, had the evidence been disclosed, the outcome of the trial would have been different. Materiality does not require that the suppressed evidence conclusively prove the defendant's innocence; rather, it must simply be significant enough that its absence undermines confidence in the verdict.
The question is not whether the defendant would more likely than not have received a different verdict with the evidence, but whether in its absence he received a fair trial, understood as a trial resulting in a verdict worthy of confidence. – Kyles v. Whitley, 514 U.S. 419 (1995)