US v. Johnson: Johnson was charged in a multi-defendant indictment with conspiracy to distribute cocaine. At trial the Government presented non-expert testimony from a DEA agent that included testimony interpreting phrases in phone conversations between Johnson and an informant. In addition, the Government presented testimony from another witness, then in prison, who claimed to have bought cocaine from Johnson years before the conspiracy at issue at trial. Johnson was convicted and sentenced to 220 months in prison.
On appeal, the Fourth Circuit reversed Johnson's conviction on two grounds. First, the court agreed with Johnson that the DEA agent's testimony violated FRE 701, in that it was lay opinion testimony (he was never certified as an expert, remember) not based on personal knowledge. The court noted that when the testimony was objected to, the Government bolstered its admissibility by asking the agent about his training and qualifications, not his relevant observations. Such "post-hoc assessments cannot be credited as a substitute for the personal knowledge and perception required under Rule 701." Second, the court agreed with Johnson that the testimony about drug transactions that occurred five years before the conspiracy allegedly began were irrelevant. As neither error was harmless, the court was required to vacate Johnson's conviction.