As an admin, I have yet to encounter a player who was able to proof to me that his stuff was stolen. I think it's too much of a hassle for admins to have to become detectives for a server to function normally.
By the way, I thought of a faster solution to this problem: Just make another faction permission module that works like the permission blocks, that way you could limit certain doors to certain ranks, or certain containers, or whatever. But this idea is so simple I can't imagine the dev team hasn't though about this before.