They wouldn't let me wash it, but on the day of the crime I had washed the floor thoroughly, and if the murderer had crossed it with his hobnailed boots, I should not have failed to see where he had been; he has left marks enough in Mademoiselle's chamber." Rouletabille rose.
"When was the last time you washed these tiles ?" he asked, and he fixed on Daddy Jacques a most searching look.
"Why--as I told you--on the day of the crime, towards half-past five--while Mademoiselle and her father were taking a little walk before dinner, here in this room: they had dined in the laboratory.

The next day, the examining magistrate came and saw all the marks there were on the floor as plainly as if they had been made with ink on white paper.
Well, neither in the laboratory nor in the vestibule, which were both as clean as a new pin, were there any traces of a man's footmarks.

Since they have been found near this window outside, he must have made his way through the ceiling of The Yellow Room into the attic, then cut his way through the roof and dropped to the ground outside the vestibule window.
But--there's no hole, neither in the ceiling of The Yellow Room nor in the roof of my attic--that's absolutely certain! So you see we know nothing--nothing! And nothing will ever be known! It's a mystery of the Devil's own making." Rouletabille went down upon his knees again almost in front of a small lavatory at the back of the vestibule.

In that position he remained for about a minute.
"Well ?" I asked him when he got up.
"Oh! nothing very important,--a drop of blood," he replied, turning towards Daddy Jacques as he spoke.

"While you were washing the laboratory and this vestibule, was the vestibule window open ?" he asked.
"No, Monsieur, it was closed; but after I had done washing the floor, I lit some charcoal for Monsieur in the laboratory furnace, and, as I lit it with old newspapers, it smoked, so I opened both the windows in the laboratory and this one, to make a current of air; then I shut those in the laboratory and left this one open when I went out.