That is very simple the "cadet" is literally government propoerty anything he/she does anywhere he/she does it is subject to/covered by the UCMJ (Uniform Code of Military Justice) regardless of who else is involved.
Only if the local authorities release jurisdiction. I had a soldier commit vehicular homicide. We had to fight the locals for jurisdiction because the homicide happened off post. Only way we were able to get it was because the night of crime began on post when he "borrowed his roommate's car without permission". I would think similar jurisdictional issues would pertain here if the crimes happened off post and the victims were no longer in the academy.