Say someone commits a crime in the military (such as embezzlement/theft/bribery whatever) but this doesn’t come to light until long after they’ve been (honorably) discharged from the military. If that person is a civilian, is he still subject to the military code of justice or is it delegated to civilian courts?
(or does his being a reservist mean he’s always military?)
As I understand it, a person can be court-martialed if they are still subject to military orders or are receiving military compensation. So a discharged veteran cannot be court-martialed, but a military retiree can be. In fact, the DC Circuit found last year that a retiree may be court-martialed for crimes committee after he or she retired.
Retired from active service, but while still subject to military orders. Reservists are considered subject to military orders as was the case in the cited decision.
“Fleet marine corps reserve” is what the marine corps calls retirement for enlisted marines who haven’t reached 30 years yet (and the Navy just calls it the “fleet reserve”). It doesn’t seem to be a legal distinction upon which the decision was based, as the same “subject to recall” logic could apply to any military retiree.
But it still doesn’t answer the question of whether someone who has left the military and is not retired or a reservist is subject to court-martial fo crimes committed prior to separating.
In WWII some merchant marine sailors though they were civilians faced court martial.
Does the military have the concept of “statute of limitations?” Answering my own question - Yes they do.
For trial by Court-Martial, the general military statute of limitations is five years (exceptions explained below). The time period starts from the day the offense is committed and stops the day that the Summary Court-Martial Convening Authority (usually the Battalion Commander) signs, or doesn’t sign, any charge sheet. Any period of AWOL or period of “fleeing justice” is excluded when counting this time period.
For any Soldier charged with AWOL/missing movement during a time of war, murder, rape, sexual assault, rape/sexual assault of a child, or with any other offense punishable by death, there is no statute of limitations. This means that for as long as the military has jurisdiction over a Soldier, he/she can be forced to face a Court-Martial for any of these offenses.
Another notable exception is for child abuse offenses. A Soldier can be forced to face a Court-Martial for these offenses for the life of the child, or 10 years, whichever is a longer period of time. For most offenses, a child is considered anyone under the age of 16.
I would think based on the above that they would not be so subject. IANAL.
So, let’s say you commit murder at Fort Bliss, and they don’t solve the case until after you are discharged. Who would have jurisdiction? The State of Texas? The U.S. 5th District court?
I think people on the Crimes Committee should be prosecuted regardless of whether or not they’re still a member. 
Apart from the court ruling, this seems like the kind of case where military jurisdiction is reasonable.
What would have happened to Larrabee if he wasn’t punished by the U.S. military? Would the Japanese authorities have prosecuted an American loosely affiliated with the U.S. military for assaulting another American with U.S. military associations?