18 U.S.C. § 1652 : US Code - Section 1652: Citizens as pirates

      Whoever, being a citizen of the United States, commits any murder
    or robbery, or any act of hostility against the United States, or
    against any citizen thereof, on the high seas, under color of any
    commission from any foreign prince, or state, or on pretense of
    authority from any person, is a pirate, and shall be imprisoned for
    life.