When the locksmith is attempting to unlock the case in the museum, he's using only a pick. Without a tension wrench, there's no way to turn the lock cylinder, so he would never succeed in picking the lock. See more
It's good, and it's bad. There's a guaranteed return, and that's good. But the guarantor is Amusa, and Amusa's a rookie, and that's bad. But it's an easily transportable object, and that's good. Only it's in a rotten position in the museum, 30 steps to the quickest exit, and that's bad. And the glass over the stone, that's bad too, because that's glass with metal mixed in it, bulletproof, shatterproof. But the locks don't look impossible, 3, maybe 5 tumblers. But there's no alarm system, and ...