In our legal system, prosecutors are constitutionally required to turn over evidence that could help clear a defendant or undermine the government’s case. Yet decades of data show that this duty is frequently violated. Withholding of exculpatory evidence – known as a Brady violation after the landmark 1963 Supreme Court case Brady v. Maryland – remains a recurring feature of the American criminal justice system. It is not the norm in every routine prosecution, but it is prevalent enough, especially in serious cases that later prove to be wrongful convictions, to exact a heavy human cost.

The National Registry of Exonerations has long identified the concealment of favorable evidence as the most common form of official misconduct in known wrongful convictions, while the largest academic study of adjudicated Brady violations finds that defendants in those cases collectively lost more than 3,800 years of freedom (https://exonerationregistry.org/sites/exonerationregistry.org/files/documents/2025Exonerations.pdf).

What the Law Requires

According to the Cornell Law School Legal Information Institute (LII):

The Brady rule, named afterBrady v. Maryland, requires prosecutors to disclose material, exculpatory information in the government’s possession to the defense. Brady material, or the evidence the prosecutor is required to disclose under this rule, includes any information favorable to the accused which may reduce a defendant’s potential sentence, go against the credibility of an unfavorable witness, or otherwise allow a jury to infer against the defendant’s guilt. (https://www.law.cornell.edu/wex/brady_rule)

It goes on further to state that:

Initially, the Brady rule was only applicable if the defendant made a pretrial request for specific information which the prosecution denied. In United States v. Bagley, however, the Supreme Court eliminated this request requirement and stated that the prosecution has a constitutional duty to disclose all material, favorable information in its possession to defendants regardless of whether it is requested. This duty is breached regardless of whether that information is withheld intentionally or unintentionally. 

If a Brady rule violation is discovered during trial, the court can either declare a mistrial or prohibit the prosecution from using unfavorable evidence that could be discredited by the withheld information. Because the Brady rule inherently involves a lack of information on the side of the defense, however, violations of the Brady rule are typically only discovered after the defendant is already convicted. As a result, the most common outcome of a Brady rule violation is overturning that conviction. Additionally, if the prosecution withheld Brady material intentionally or knowingly, they may be subject to sanctions. (https://www.law.cornell.edu/wex/brady_rule)

The burden of proof falls upon the defense to prove a Brady violation occurred:

The defendant bears the burden to prove that any withheld information was both material and favorable. A defendant meets this burden if they can show that there is a reasonable probability that the outcome of the trial would have been different had the information been disclosed. In Kyles v. Whitley, the Supreme Court clarified four aspects of this test: 

1. “Reasonable probability” is a question of whether the government’s failure to disclose this information undermines confidence in the outcome of the trial.
2. “Reasonable probability” is not a sufficiency of evidence test, and the defendant does not need to show that the evidence, barring any evidence undermined by the withheld information, is inadequate to support a conviction. Rather, the defendant merely must show that the withheld information can reasonably be taken to put the whole case in a different light. 
3. Failure to disclose information which has a reasonable probability of changing the outcome of the trial is inherently harmful; thus there is no need for a separate harmless error review. 
4. All information not disclosed must be considered collectively, not item by item. (https://www.law.cornell.edu/wex/brady_rule)