With the scrunity and the attention on of handling of K.I.A.'s these days by the military I doubt it came from there as smuggling. Too many risk factors. Likely an old box. In equipment being shipped back? Sure likely being done.
Where's there? I'm thinking it was shipped back from Central America/Mexico. Some paper work showing an active duty death from natural causes, being shipped to home town funeral parlor or some such thing. Dead cat gives a slight odor of death, maybe cause someone to not consider opening it. Just a thought, they'll do anything to get drugs in. $$$$$$