“Oh! no, not at all. I have plenty more. For instance, after the crime, you went out the same way you had entered. But, in the centre of the wardrobe-room, being seized by some sudden fear, you leaned against the wall for support.”

“How do you know that? No one could know such a thing,” argued the desperate man.

“The police know nothing about it, of course. They never think of lighting a candle and examining the walls. But if they had done so, they would have found on the white plaster a faint red spot, quite distinct, however, to trace in it the imprint of your thumb which you had pressed against the wall while it was wet with blood. Now, as you are well aware, under the Bertillon system, thumbmarks are one of the principal means of identification.”