The Brady doctrine requires prosecutors to disclose all favorable and material evidence to the defense. To effectuate that rule, the U.S. Supreme Court has defined materiality as a “reasonable probability” that the evidence would have affected the outcome at trial. But apart from that definition, the Court has resisted offering any further guidance to lower courts. While far too little is known about how Brady materiality claims are actually adjudicated, there is strong evidence that courts often reject Brady claims involving withheld evidence on the grounds that the evidence was not significant enough to be material.

To examine how Brady materiality questions are decided, we utilize a unique database of five years of Brady rulings in state and federal courts. We analyze over 100 recent rulings in which courts rejected Brady claims because the withheld evidence, while favorable to the defendant, was not material. We also compare these rejected Brady claims to dozens of cases in which courts found evidence to be material and thus a Brady violation. Our data indicates that while the Brady doctrine covers both exculpatory and impeachment evidence, courts frequently reject evidence that would have been used to impeach a witness on materiality grounds. We also document that many courts correctly state the legal standard for materiality, but they then apply it incorrectly. Rather than conducting an evidence-based analysis that focuses on the value of the withheld evidence, courts often engage in guilt-based reasoning that improperly focuses on the strength of the evidence presented at trial.

To improve the reliability of judicial rulings in Brady cases, we propose that courts focus on empirical evidence of how reasonable jurors actually weigh evidence in criminal trials. We further suggest statutory reforms to the federal habeas corpus rules. For too long, materiality standards in the Brady context, and in other constitutional criminal procedure and post-conviction contexts, have been applied inconsistently and contrary to established doctrine. A renewed focus on how judges apply the Brady materiality standard is long overdue.

* Garrett is the David W. Ichel Distinguished Professor of Law, Duke University School of Law and Faculty Director, Wilson Center for Science and Justice. Gershowitz is the James D. & Pamela J. Penny Research Professor and Hugh & Nolie Haynes Professor of Law, William and Mary Law School. Our thanks to Jennifer Teitcher and Michael Heise for helpful conversations, to Ryan Zimmerman for excellent research assistance, and to Don Hopkins and Sean Chen of the Duke Law Library for building the Brady database website that hosts all of the cases discussed here.