If they'd put some kind of security in place, but the clever professionals employed by the millionaire collectors had fooled them, that might be some kind of excuse. But since there doesn't appear to have been any attempt by the occupying army to protect the buildings in question or their contents, it doesn't really make any difference whatsoever. "I know I didn't bother to shut my front door, but you can't blame me for the burgalry - the burglar could very likely have been able to pick the lock anyway."

"Sophisticated malfeasance"? I imagine that would be if there was a suggestion that it was a put up job by people high up in the army to obtain the loot, with them arranging not to have guards on the doors, and trashing the place as a cover up. I know that kind of thing is a standard plot in Hollywood caper movies, where it's all presented as a jolly game, but I'm inclined to doubt if anything as sophisticated as that is involved.