Which rule governs impeachment of witness credibility in trial?

• A. Jencks Act
• B. Giglio
• C. Rule 16
• D. Surveillance

Answer: (B)

Impeachment of witness credibility hinges on revealing information that could show a witness is biased or has an incentive to lie. The key rule here is from Giglio v. United States, which requires prosecutors to disclose to the defense any information that could impeach a witness’s credibility—such as deals, promises of immunity or favorable treatment in exchange for testimony, or other biases and relationships that might affect truthfulness. This ensures the defense can effectively test reliability during cross-examination and helps guarantee a fair trial. The Jencks Act, while related to a witness’s prior statements, focuses on the production of those statements after testimony rather than a broad obligation to disclose impeachment material. Rule 16 covers discovery generally but is not specific to impeachment credibility, and surveillance is not a rule governing impeachment.