The detective looked puzzled. “What about them?” he asked.
“They were made with stamps—two stamps, as a matter of fact—and those stamps were made by photographic process from the official finger-print form. I can prove that beyond all doubt.”
“Well, suppose they were. What then?”
Thorndyke opened a drawer and took out a photograph, which he handed to Miller. “Here,” he said, “is the photograph of the official finger-print form which you were kind enough to bring me. What does it say at the bottom there?” and he pointed with his finger.
The superintendent read aloud: “Impressions taken by Joseph Woodthorpe. Rank, Warder; Prison, Holloway.” He stared at the photograph for a moment, and then exclaimed—
“Well, I’m hanged! You have worked this out neatly, doctor! and so quick too. We’ll have Mr. Woodthorpe under lock and key the first thing to-morrow morning. But how did he do it, do you think?”
“He might have taken duplicate finger-prints and kept one form; the prisoners would not know there was anything wrong; but he did not in this case. He must have contrived to take a photograph of the form before sending it in—it would take a skilful photographer only a minute or two with a suitable hand-camera placed on a table at the proper distance from the wall; and I have ascertained that he is a skilful photographer. You will probably find the apparatus, and the stamps too, when you search his rooms.”
“Well, well. You do give us some surprises, doctor. But I must be off now to see about this warrant. Good-night, sir, and many thanks for your help.”
When the superintendent had gone we sat for a while looking at one another in silence. At length Thorndyke spoke. “Here is a case, Jervis,” he said, “which, simple as it is, teaches a most invaluable lesson—a lesson which you should take well to heart. It is this: The evidential value of any fact is an unknown quantity until the fact has been examined. That seems a self-evident truth, but like many other self-evident truths, it is constantly overlooked in practice. Take this present case. When I left Caldwell’s house this morning the facts in my possession were these: (1) The man who murdered Caldwell was directly or indirectly connected with the Finger-print Department. (2) He was almost certainly a skilled photographer. (3) He probably committed the Winchmore Hill and the other burglaries. (4) He was known to Caldwell, had had professional dealings with him and was probably being blackmailed. This was all; a very vague clue, as you see.
“There was the handkerchief, planted, as I had no doubt, but could not prove; the name stamped on it was Belfield’s, but any one can get a rubber stamp made. Then it was stained with blood, as handkerchiefs often are; that blood might or might not be human blood; it did not seem to matter a straw whether it was or not. Nevertheless, I said to myself: If it is human, or at least mammalian blood, that is a fact; and if it is not human blood, that is also a fact. I will have that fact, and then I shall know what its value is. I examined the stain when I reached home, and behold! it was camel’s blood; and immediately this insignificant fact swelled up into evidence of primary importance. The rest was obvious. I had seen Woodthorpe’s name on the form, and I knew several other officials. My business was to visit all places in London where there were camels, to get the names of all persons connected with them and to ascertain if any among them was a photographer. Naturally I went first to the Zoo, and at the very first cast hooked Joseph Woodthorpe. Wherefore I say again: Never call any fact irrelevant until you have examined it.”