Which case requires disclosure of impeachment information by prosecutors?

• A. Giglio v. United States
• B. Miranda v. Arizona
• C. Brady v. Maryland
• D. Mapp v. Ohio

Answer: (A)

Impeachment information must be disclosed by prosecutors to ensure the defense can assess a witness’s credibility. In Giglio v. United States, the Supreme Court ruled that the prosecution must reveal impeachment material—such as promises of leniency, deals, or inducements given to a witness, or evidence of bias and prior inconsistent statements—if it could affect the witness’s credibility and is material to the case. This requirement extends Brady’s broader rule about prosecutorial disclosure by moving the focus to how credible a witness is, not just whether the testimony is exculpatory.

Brady v. Maryland sets the baseline by requiring disclosure of favorable exculpatory evidence, but it is Giglio that specifically handles impeachment and credibility-related material. The other cases address different protections: Miranda v. Arizona concerns warnings during custodial interrogation, and Mapp v. Ohio concerns the exclusionary rule for illegally obtained evidence.