The Red Thumb Mark

by R. Austin Freeman

"Thank you," said the judge, with a bland smile; "we will accept your sworn testimony unless the learned counsel for the prosecution demands verification."

He received the photographs which Thorndyke handed up and, having examined them with close attention, passed them on to the jury.

"The third fact," resumed Thorndyke, "is of much more importance, since it not only proves the print to be a forgery, but also furnishes a very distinct clue to the origin of the forgery, and so to the identity of the forger." (Here the court became hushed until the silence was so profound that the ticking of the clock seemed a sensible interruption. I glanced at Walter, who sat motionless and rigid at the end of the bench, and perceived that a horrible pallor had spread over his face, while his forehead was covered with beads of perspiration.) "On looking at the print closely, I noticed at one part a minute white mark or space. It was of the shape of a capital S and had evidently been produced by a defect in the paper—a loose fibre which had stuck to the thumb and been detached by it from the paper, leaving a blank space where it had been. But, on examining the paper under a low power of the microscope, I found the surface to be perfect and intact. No loose fibre had been detached from it, for if it had, the broken end or, at least, the groove in which it had lain, would have been visible. The inference seemed to be that the loose fibre had existed, not in the paper which was found in the safe, but in the paper on which the original thumb-mark had been made. Now, as far as I knew, there was only one undoubted thumb-print of Reuben Hornby's in existence—the one in the 'Thumbograph.' At my request, the 'Thumbograph' was brought to my chambers by Mrs. Hornby, and, on examining the print of Reuben Hornby's left thumb, I perceived on it a minute, S-shaped white space occupying a similar position to that in the red thumb-mark; and when I looked at it through a powerful lens, I could clearly see the little groove in the paper in which the fibre had lain and from which it had been lifted by the inked thumb. I subsequently made a systematic comparison of the marks in the two thumb-prints; I found that the dimensions of the mark were proportionally the same in each—that is to say, the mark in the 'Thumbograph' print had an extreme length of 26/1000 of an inch and an extreme breadth of 14.5/1000 of an inch, while that in the red thumb-mark was one-fortieth larger in each dimension, having an extreme length of 26.65/1000 of an inch and an extreme breadth of 14.86/1000 of an inch; that the shape was identical, as was shown by superimposing tracings of greatly enlarged photographs of each mark on similar enlargements of the other; and that the mark intersected the ridges of the thumb-print in the same manner and at exactly the same parts in the two prints."

"Do you say that—having regard to the facts which you have stated—it is certain that the red thumb-mark is a forgery?"

"I do; and I also say that it is certain that the forgery was executed by means of the 'Thumbograph.'"

"Might not the resemblances be merely a coincidence?"

"No. By the law of probabilities which Mr. Singleton explained so clearly in his evidence, the adverse chances would run into untold millions. Here are two thumb-prints made in different places and at different times—an interval of many weeks intervening. Each of them bears an accidental mark which is due not to any peculiarity of the thumb, but to a peculiarity of the paper. On the theory of coincidences it is necessary to suppose that each piece of paper had a loose fibre of exactly identical shape and size and that this fibre came, by accident, in contact with the thumb at exactly the same spot. But such a supposition would be more opposed to probabilities even than the supposition that two exactly similar thumb-prints should have been made by different persons. And then there is the further fact that the paper found in the safe had no loose fibre to account for the mark."

"What is your explanation of the presence of defibrinated blood in the safe?"

"It was probably used by the forger in making the thumb-print, for which purpose fresh blood would be less suitable by reason of its clotting. He would probably have carried a small quantity in a bottle, together with the pocket slab and roller invented by Mr. Galton. It would thus be possible for him to put a drop on the slab, roll it out into a thin film and take a clean impression with his stamp. It must be remembered that these precautions were quite necessary, since he had to make a recognisable print at the first attempt. A failure and a second trial would have destroyed the accidental appearance, and might have aroused suspicion."

"You have made some enlarged photographs of the thumb-prints, have you not?"