In United States v. Thompson, 379 F.2d 625, 627 (6th Cir. 1967), appellant's perjury conviction was based on the testimony of one police officer, and the testimony of two FBI agents. The appellant claimed that he had requested that the police officer contact his attorney, but the police officer testified that a conversation to that effect never took place. Id. at 626-27. The FBI agents were not present when the conversation was alleged to have taken place, and thus could corroborate neither the officer's nor the appellant's version of events. Id. at 626-27. The court concluded that the evidence was insufficient under the two-witness rule, because the FBI agents' testimony did not substantiate a material issue in the case. Id. at 628.