“It is of the highest importance in the art of detection to be able to recognise, out of a number of facts, which are incidental and which vital. Otherwise your energy and attention must be dissipated instead of being concentrated. Now, in this case there was not the slightest doubt in my mind from the first that the key of the whole matter must be looked for in the scrap of paper in the dead man’s hand.
“Before going into this, I would draw your attention to the fact that, if Alec Cunningham’s narrative was correct, and if the assailant, after shooting William Kirwan, had instantly fled, then it obviously could not be he who tore the paper from the dead man’s hand. But if it was not he, it must have been Alec Cunningham himself, for by the time that the old man had descended several servants were upon the scene. The point is a simple one, but the Inspector had overlooked it because he had started with the supposition that these county magnates had had nothing to do with the matter. Now, I make a point of never having any prejudices, and of following docilely wherever fact may lead me, and so, in the very first stage of the investigation, I found myself looking a little askance at the part which had been played by Mr. Alec Cunningham.
“And now I made a very careful examination of the corner of paper which the Inspector had submitted to us. It was at once clear to me that it formed part of a very remarkable document. Here it is. Do you not now observe something very suggestive about it?”