"The thumb-mark is that of Reuben Hornby, a fact that establishes a prima facie probability that he stole the diamonds. But there is no evidence that he had access to them, and if he had not, he could not have made the thumb-mark in the manner and at the time stated.
"But John Hornby may have had access to the previously-made thumb-mark of Reuben, and may possibly have obtained it; in which case he is almost certainly the thief.
"As to Walter Hornby, he may have had the means of obtaining Reuben's thumb-mark; but there is no evidence that he had access either to the diamonds or to Mr. Hornby's memorandum block. The prima facie probabilities in his case, therefore, are very slight."
"The actual points at issue, then," I said, "are, whether Reuben had any means of opening the safe, and whether Mr. Hornby ever did actually have the opportunity of obtaining Reuben's thumb-mark in blood on his memorandum block."
"Yes," replied Thorndyke. "Those are the points—with some others—and they are likely to remain unsettled. Reuben's rooms have been searched by the police, who failed to find any skeleton or duplicate keys; but this proves nothing, as he would probably have made away with them when he heard of the thumb-mark being found. As to the other matter, I have asked Reuben, and he has no recollection of ever having made a thumb-mark in blood. So there the matter rests."
"And what about Mr. Hornby's liability for the diamonds?"
"I think we may dismiss that," answered Thorndyke. "He had undertaken no liability and there was no negligence. He would not be liable at law."
After my colleague retired, which he did quite early, I sat for a long time pondering upon this singular case in which I found myself involved. And the more I thought about it the more puzzled I became. If Thorndyke had no more satisfactory explanation to offer than that which he had given me this evening, the defence was hopeless, for the court was not likely to accept his estimate of the evidential value of finger-prints. Yet he had given Reuben something like a positive assurance that there would be an adequate defence, and had expressed his own positive conviction of the accused man's innocence. But Thorndyke was not a man to reach such a conviction through merely sentimental considerations. The inevitable conclusion was that he had something up his sleeve—that he had gained possession of some facts that had escaped my observation; and when I had reached this point I knocked out my pipe and betook myself to bed.