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
