United States v. Bagley
The Supreme Court ruled that a conviction should only be overturned for withheld evidence favoring the defense if there is a "reasonable probability" that disclosing it would have changed the trial's outcome — the same standard whether the evidence would have proven innocence or just challenged a witness's credibility.
The decision rejected a lower court's rule that automatically reverses convictions whenever prosecutors ignore a specific defense request for evidence useful in cross-examining witnesses, sending the case back for the Ninth Circuit to apply the new standard.
“A "reasonable probability" is a probability sufficient to undermine confidence in the outcome.”
The Court's core definition of when withheld evidence requires a new trial.
How it got here: A federal judge denied Bagley's request to vacate his sentence; the Ninth Circuit reversed and ordered automatic reversal; the government asked the Supreme Court to review that ruling.
The Case in Depth
What happened
Hughes Bagley was charged with federal drug and gun violations based largely on the testimony of two private security guards who worked undercover for federal agents. Before trial, Bagley's lawyer asked prosecutors to disclose any deals or rewards promised to witnesses. Years after his conviction, Bagley learned through public-records requests that the two guards had signed contracts promising them payment for their assistance, which had never been disclosed to him.
The question before the Court
If prosecutors don't hand over requested evidence that could be used to question a witness's honesty, how likely must it be that this would have changed the trial's result before the conviction must be thrown out?
Why it matters
Defendants across the country rely on prosecutors to turn over evidence that could undercut government witnesses, including secret payments or deals. This ruling means that even when prosecutors wrongly withhold such evidence, a conviction stands unless the defendant can show a real chance the outcome would have been different \u2014 a standard that shapes how courts review nondisclosure claims in criminal appeals nationwide.
What changes now
The case returns to the Ninth Circuit, which must now decide, under the Court's new "reasonable probability" standard, whether disclosure of the payment agreements to the two witnesses would likely have changed the outcome of Bagley's trial. This is a final merits ruling on the legal standard, but it does not resolve whether Bagley's conviction will ultimately stand or be overturned; that determination is left to the lower court on remand.
What this does not decide
The Court did not decide whether the withheld evidence in this case actually would have changed the trial's outcome — it sent that fact-specific question back to the Ninth Circuit. It also did not adopt Justice Marshall's or Justice Stevens's view that specific defense requests deserve extra protection beyond the single materiality standard.
Concurrences and dissents
Concurrence — Justice White
Justice White agreed with the majority's core holding that undisclosed evidence must be "material" under a reasonable-probability standard, and joined the background discussion of Brady's history. But he declined to address how the specificity of a defense request should factor into the analysis, preferring a simple rule that all cases share the same reasonable-probability test.
Dissent — Justice Marshall
“The prosecutor, convinced of the guilt of the defendant and of the truthfulness of his witnesses, may all too easily view as irrelevant or unpersuasive evidence that draws his own judgments into question.”Marshall's objection that the new standard lets prosecutors decide for themselves what evidence matters.
Justice Marshall argued that withholding evidence impeaching the government's only witnesses can never be harmless error, and would have affirmed the Ninth Circuit's reversal outright rather than remanding. He also argued more broadly that prosecutors should have to disclose all evidence that might reasonably favor the defense, with only harmless-error review (not a strict pretrial materiality test) protecting convictions, since retrospective materiality standards let prosecutors gamble on withholding evidence.
Dissent — Justice Stevens
Justice Stevens agreed the Ninth Circuit misapplied the law but objected to the majority rewriting the Brady rule itself. He argued that specific-request cases like this one should keep a more defense-friendly "reasonable likelihood" standard distinct from the stricter no-request standard from Agurs, and would have remanded under that older framework rather than the Court's new single test.
How the Court got there
The legal reasoning, step by step
- The Court began from the rule that hiding evidence favorable to a defendant violates due process only when that evidence is "material" — meaning its disclosure might have changed the outcome — not simply whenever anything favorable goes undisclosed.
- The Court rejected the idea that evidence used to challenge a witness's credibility deserves a different, stricter rule than evidence directly proving innocence, holding that both kinds of favorable evidence are governed by the same materiality test.
- The Court also rejected the lower court's reliance on cases about denying a defendant the chance to cross-examine a witness at all, explaining that Bagley's lawyer was free to question the witnesses — the problem here was only that the government didn't share information that would have made that questioning more effective.
- Borrowing the test used for claims of incompetent defense lawyers, the Court adopted a single materiality standard: evidence is material only if there is a "reasonable probability" that disclosing it would have changed the result of the proceeding, meaning a probability sufficient to undermine confidence in the outcome.
- The Court held this flexible standard applies regardless of whether the defense made no request, a general request, or (as here) a specific request for the evidence, though a reviewing court may weigh how a specific request affected the defense's trial strategy.
- Because the lower appeals court had not applied this standard and had instead ordered automatic reversal, the Court sent the case back for the Ninth Circuit to decide whether disclosure of the witnesses' payment agreements would likely have changed the trial's result.
Doctrinal impact
Cases affected by this decision
Limits United States v. Agurs (427 U.S. 97)
Replaces Agurs's three separate disclosure standards with one single reasonable-probability materiality test for all cases.
Reaffirms Giglio v. United States (405 U.S. 150)
Confirms that hidden deals affecting a witness's credibility are treated the same as other favorable evidence under Brady.
Distinguishes Davis v. Alaska (415 U.S. 308)
Says this case, unlike Davis, involved no direct court-imposed limit on cross-examination, so automatic reversal doesn't apply.