United States v. Copelin
United States Court of Appeals for the District of Columbia Circuit
996 F.2d 379 (D.C. Cir. 1993)
Copelin (defendant), charged with distributing cocaine, claimed at trial that another man he was with had actually been the one selling the drugs. On cross-examination, when Copelin denied ever seeing drugs change hands and claimed he had only ever seen drugs on television, the prosecution introduced evidence that Copelin had tested positive for cocaine multiple times, to contradict his claim that he'd never seen drugs in person. The trial court admitted this evidence but did not instruct the jury that it could be used only to assess Copelin's credibility, and Copelin was convicted.
Whether a witness's own prior positive drug tests are admissible to impeach his trial testimony that he had never seen drugs outside of television, and whether the jury must be instructed to consider that evidence only for impeachment.