“I know no more than you do, Fanferlot; and you seem to have made up your mind, whereas I am still undecided.  You declare the cashier to be innocent, and the banker guilty.  I don’t know whether you are right or wrong.  I started after you, and have only reached the preliminaries of my search.  I am certain of but one thing, and that is, that a scratch was on the safe-door.  That scratch is my starting-point.”

As he spoke, M. Lecoq took from his desk and unrolled an immense sheet of drawing-paper.

On this paper was photographed the door of M. Fauvel’s safe.  The impression of every detail was perfect.  There were the five movable buttons with the engraved letters, and the narrow, projecting brass lock:  The scratch was indicated with great exactness.

“Now,” said M. Lecoq, “here is our scratch.  It runs from top to bottom, starting from the hole of the lock, diagonally, and, observe, from left to right; that is to say, it terminates on the side next to the private staircase leading to the banker’s apartments.  Although very deep at the key-hole, it ends off in a scarcely perceptible mark.”

“Yes, patron, I see all that.”

“Naturally you thought that this scratch was made by the person who took the money.  Let us see if you were right.  I have here a little iron box, painted with green varnish like M. Fauvel’s safe; here it is.  Take a key, and try to scratch it.”

“The deuce take it!” he said after several attempts, “this paint is awfully hard to move!”

“Very hard, my friend, and yet that on the safe is still harder and thicker.  So you see the scratch you discovered could not have been made by the trembling hand of a thief letting the key slip.”

“Sapristi!” exclaimed Fanferlot, stupefied:  “I never should have thought of that.  It certainly required great force to make the deep scratch on the safe.”

“Yes, but how was that force employed?  I have been racking my brain for three days, and only yesterday did I come to a conclusion.  Let us examine together, and see if our conjectures present enough chances of probability to establish a starting-point.”

M. Lecoq abandoned the photograph, and, walking to the door communicating with his bedroom, took the key from the lock, and, holding it in his hand, said: 

“Come here, Fanferlot, and stand by my side:  there; very well.  Now suppose that I want to open this door, and you don’t want me to open it; when you see me about to insert the key, what would be your first impulse?”

“To put my hands on your arm, and draw it toward me so as to prevent your introducing the key.”

“Precisely so.  Now let us try it; go on.”  Fanferlot obeyed; and the key held by M. Lecoq, pulled aside from the lock, slipped along the door, and traced upon it a diagonal scratch, from top to bottom, the exact reproduction of the one in the photograph.

“Oh, oh, oh!” exclaimed Fanferlot in three different tones of admiration, as he stood gazing in a revery at the door.