10 U.S.C. § 12684

The President or the Secretary concerned may drop from the rolls of the armed force concerned any Reserve— (1) who has been absent without authority for at least three months; (2) who may be separated under section 12687 of this title by reason of a sentence to confinement adjudged by a court-martial; or (3) who is sentenced to confinement in a Federal or State penitentiary or correctional institution after having been found guilty of an offense by a court other than a court-martial or other military court, and whose sentence has become final.