Brady and Giglio : The Prosecution's Duty to Disclose Favorable Evidence

The Brady Rule

The State doesn't just have to share the evidence it plans to use — it has an affirmative constitutional duty to disclose evidence that helps the defense. Under Brady v. Maryland, suppressing evidence favorable to the accused violates due process when the evidence is material — meaning there's a reasonable probability it could have affected the outcome. This applies whether the defense asked for it or not, and whether the suppression was intentional or not.

The Giglio Extension: Impeachment Evidence

Giglio v. United States made clear that Brady covers impeachment evidence, not just evidence of innocence. That includes:

• Deals, promises, or leniency given to a cooperating witness in exchange for testimony;
• Prior inconsistent statements by a State's witness;
• A witness's bias, motive to lie, or credibility problems;
• An officer's documented dishonesty or misconduct that bears on credibility (sometimes maintained on so-called "Brady/Giglio lists").

If the State's case depends on a witness, evidence that undermines that witness can be just as valuable as evidence about the offense itself.

It's the Prosecution's Duty — and It's Ongoing

The duty rests on the prosecution, and it extends to favorable evidence known to others acting on the government's behalf, including police. It is also continuing: if favorable evidence surfaces later, it must be disclosed then. A defendant who suspects favorable evidence is being withheld can move to compel disclosure and, where appropriate, ask the court to review materials.

What Happens When the Duty Is Violated

Remedies depend on timing and prejudice. Before or during trial, the court can order disclosure, grant a continuance, or exclude evidence. After a conviction, a genuine Brady violation — favorable, suppressed, material evidence — can be grounds to overturn the result. The seriousness of the remedy reflects how central these disclosure duties are to a fair trial.