The "two witness" rule, derived from common law, governs the proof required for a perjury conviction under Section 1621. Weiler v. United States, 323 U.S. 606, 609 (1945). The rule means that a perjury conviction may not rest solely on the uncorroborated testimony of one witness. United States v. Hammer, 271 U.S. 620, 626 (1926). The two witness rule, however, does not require two witnesses to every perjurious statement. The falsity of the perjurious statement may be established either by the testimony of two independent witnesses or by one witness and independent corroborating evidence that is inconsistent with the innocence of the accused. Weiler, 323 U.S. at 610. Also, the second witness need not fully corroborate the first, but must substantiate the other's testimony concerning the defendant's perjurious statement. United States v. Chaplin, 25 F.3d 1373, 1381-82 (7th Cir. 1994). The two witness rule does not apply if the perjurious statement concerns the defendant's state of mind (usually lack of memory), which can be established by circumstantial evidence. Id. at 1378. The two witness rule also does not apply to sentence enhancements for obstruction of justice, even if based on the defendant's perjury at trial. United States v. Onumonu, 999 F.2d 43, 46 (2d Cir. 1993).
The two witness rule does not apply to section 1623 prosecutions. Section 1623(e) expressly eliminates the two witness rule for prosecutions under that statute. Moreover, Section 1623(c) allows prosecutions for making two or more statements under oath that are inconsistent to the degree that one of them is necessarily false. In such prosecutions, the government does not have to prove which irreconcilably contradictory declaration was false. United States v. McAfee, 8 F.3d 1010, 1014 (5th Cir. 1993). In inconsistent declaration prosecutions, Congress expressly provided a defense when "the defendant at the time he made each declaration believed the declaration was true." United States v. Porter, 994 F.2d 470, 473 (8th Cir. 1993)(conviction reversed; questions not irreconcilably in conflict). Each of the irreconcilably inconsistent statements also must be within the statute of limitations. Id. at 472.
[cited in USAM 9-69.200]