I don't think there are many hands in the world of that sort.
It is big and strong and the fingers are nearly all one as long as the other! The thumb is wanting and we have only the mark of the palm; but if we follow the trace of the hand," I continued, "we see that, after leaving its imprint on the wall, the touch sought the door, found it, and then felt for the lock--" "No doubt," interrupted Rouletabille, chuckling,--"only there is no blood, either on the lock or on the bolt!" "What does that prove ?" I rejoined with a good sense of which I was proud; "he might have opened the lock with his left hand, which would have been quite natural, his right hand being wounded." "He didn't open it at all!" Daddy Jacques again exclaimed.

"We are not fools; and there were four of us when we burst open the door!" "What a queer hand!--Look what a queer hand it is!" I said.
"It is a very natural hand," said Rouletabille, "of which the shape has been deformed by its having slipped on the wall.

The man dried his hand on the wall.

He must be a man about five feet eight in height." "How do you come at that ?" "By the height of the marks on the wall." My friend next occupied himself with the mark of the bullet in the wall.
It was a round hole.
"This ball was fired straight, not from above, and consequently, not from below." Rouletabille went back to the door and carefully examined the lock and the bolt, satisfying himself that the door had certainly been burst open from the outside, and, further, that the key had been found in the lock on the inside of the chamber.

He finally satisfied himself that with the key in the lock, the door could not possibly be opened from without with another key.