Impeachment of government witness credibility is associated with which case?

• A. Giglio v. United States
• B. Jencks Act
• C. Exculpatory evidence
• D. Direct evidence

Answer: (A)

Disclosing information that could impeach a government witness’s credibility is required of prosecutors. This principle comes from Giglio v. United States, which held that any evidence affecting a witness’s credibility—such as plea deals, immunity, or other bias—must be disclosed to the defense. It extends Brady’s fairness guarantee by ensuring the defense can assess reliability and cross-examine effectively. The Jencks Act governs the production of a witness’s prior statements after they testify, not the broader obligation to reveal credibility-affecting information. Exculpatory evidence is favorable to the defense in general, not specifically about a witness’s credibility, and direct evidence is simply evidence that directly proves a fact, not a case name or doctrine. So, the case tied to impeachment of government witness credibility is Giglio v. United States.