Alford v. United States
In Alford v. United States, 282 U.S. 687 (1931), the United States Supreme Court held that the trial court erred in preventing the defendant from engaging in cross-examination of a prosecution witness that would show that the witness was then in custody for a pending criminal charge.
This evidence was admissible, the Court held, to show that the witness's testimony "was biased because given under promise or expectation of immunity, or under the coercive effect of his detention by officers of the United States, which was conducting the present prosecution. . . . Petitioner was entitled to show by cross-examination that the witness's testimony was affected by fear or favor growing out of his detention." Id. at 693.