It fitted, and he opened the box, but after a moment's hesitation, closed and relocked it, and slipped the bunch of keys, as well as the key that had originally stood in the lock, into his own pocket. 
He couldn't find a key to work in the box.
mnli hypothesis: He couldn't find a key to work in the box. premise: It fitted, and he opened the box, but after a moment's hesitation, closed and relocked it, and slipped the bunch of keys, as well as the key that had originally stood in the lock, into his own pocket. 