“Yes, I see.  Then you consider my theory of John Hornby as the perpetrator of the robbery as quite a tenable one?” “Quite,” replied Thorndyke.  “I have entertained it from the first; and the new facts that you have gathered increase its probability.  You remember I said that four hypotheses were possible:  that the robbery was committed either by Reuben, by Walter, by John Hornby, or by some other person.  Now, putting aside the ‘some other person’ for consideration only if the first three hypotheses fail, we have left, Reuben, Walter, and John.  But if we leave the thumb-print out of the question, the probabilities evidently point to John Hornby, since he, admittedly, had access to the diamonds, whereas there is nothing to show that the others had.  The thumb-print, however, transfers the suspicion to Reuben; but yet, as your theory makes evident, it does not completely clear John Hornby.  As the case stands, the balance of probabilities may be stated thus:  John Hornby undoubtedly had access to the diamonds, and therefore might have stolen them.  But if the thumb-mark was made after he closed the safe and before he opened it again, some other person must have had access to them, and was probably the thief.

“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.”