5 U.S.C. § 303: Oaths to witnesses

(a) An employee of an Executive department lawfully assigned to investigate frauds on or attempts to defraud the United States, or irregularity or misconduct of an employee or agent of the United States, may administer an oath to a witness attending to testify or depose in the course of the investigation. (b) An employee of the Department of Defense lawfully assigned to investigative duties may administer oaths to witnesses in connection with an official investigation.