18 U.S. Code § 3049 - Warrant for removal
Only one writ or warrant is necessary to remove a prisoner from one district to another. One copy thereof may be delivered to the sheriff or jailer from whose custody the prisoner is taken, and another to the sheriff or jailer to whose custody he is committed, and the original writ, with the marshal’s return thereon, shall be returned to the clerk of the district to which he is removed.
Based on title 18, U.S.C., 1940 ed., § 604 (R.S. § 1029).