Sections 1621 and 1623(a) both explicitly cross-reference 28 U.S.C. § 1746. Congress added 18 U.S.C. § 1746 in 1976 to allow certain unsworn declarations to be made subject to the penalties of perjury. Case law concerning section 1746 declarations is extremely limited and generally concerns whether unsworn declarations can be submitted in particular proceedings. Section 1746 declarations are prosecutable as perjury, even though the law did not require the original declaration under penalty of perjury, to be sworn. United States v. Gomez-Vigil, 929 F.2d 254, 257 (6th Cir. 1991). These declarations may be scrutinized by the courts. For example, the United States Court of Appeals for the Ninth Circuit overturned a section 1623(c) conviction because one witness statement at issue was not under oath, but was taken under section 1746. United States v. Jaramillo, 69 F.3d 388, 390-91 (9th Cir. 1995). The court determined that Congress required section 1623(c) inconsistent statement prosecutions to meet stringent requirements and that since only section 1623(a) referred expressly to section 1746, unsworn declarations did not meet section 1623(c)'s requirements.
[cited in USAM 9-69.200]