The third element of a perjury offense is proof of specific intent, that is, that the defendant made the false statement with knowledge of its falsity, rather than as a result of confusion, mistake or faulty memory. United States v. Dunnigan, 507 U.S. 87, 94 (1993). Section 1621 requires that the defendant have acted "willfully"; the section 1623 requirement is to act "knowingly." In practice, these standards are virtually identical, although the government need not prove both willfulness and knowledge to sustain a section 1623 prosecution. United States v. Fornaro, 894 F.2d 508, 512 (2d Cir. 1990). Under either statute, the government must demonstrate the defendant voluntarily made the false statement with knowledge of its falsity. If the defendant believed his or her statement to be true when it was made, even though it was false, this essential element will not have been proven. See this Manual at 1753.
[cited in USAM 9-69.200]