"As I put the rifle down on the bare deal table which forms the principal piece of furniture in the gun-room, I saw a grain of something dark, which looked like earth, fall off the butt end on to the boards beneath. I picked up the rifle, and looked closely at the butt; it was criss-crossed with small cuts, as they sometimes are, with the idea of preventing them from slipping, and in the cuts some dust, or earth, seemed, as I expected, to be adhering. I knocked the rifle upon the table, and a little shower fell from it. Except for the first grain, it might have been nothing but the ordinary dust of disuse, but I could not help thinking it was of a darker hue than the accumulations of years generally take upon themselves, and, further, I knew that the rifle had lately been used for stalking. It was, moreover, specklessly clean in every other part. I felt certain it had been leant upon the ground at no distant date; and I remembered the mark I had not been able to account for at the foot of the rose-bush, near the place where the plank had been used and, as I was persuaded, the cowardly shot actually fired. If a gun had been leant up against the large standard rose that grew there, it would have left just such a mark upon the soft ground.
"All this, of course, was a mere surmise, and rather wild at that, but the deer forests of Scotland are not muddy, whatever else they may be, and I felt an unreasoning conviction that the rifle had not accumulated dust while engaged upon its legitimate business on the mountain tops. The peaty moorland soil on which the castle stood would hardly be the best thing in the world for rose-trees, I imagined, and it seemed not too much to hope that some other kind of earth might be artificially mingled with it. I carefully collected the dust in a pill-box, and promised myself to lose no time in obtaining the opinion of an expert analyst, as to whether or no some trace of patent fertilizer, or other chemical, could not be traced in it.
"It was now for the first time that suspicion of young Lord Ashiel began to oust my theory of the Nihilist society's responsibility for the murder. He had, as I remembered, struck me as taking his cousin's guilt for granted with somewhat unnecessary alacrity. His rifle, I already believed, perhaps in my turn with needless alacrity, had fired the fatal bullet, and it seemed perfectly possible that it was his finger that pressed upon the trigger. He was, I knew, in the billiard-room, and alone, both before and after the murder was committed. It would have been quite easy for him to fetch his rifle, place the gardener's plank in position, fire his shot and return to the house, provided Miss Byrne did not rush immediately from the room. He knew her to be a brave girl and not likely to fly without making some attempt at offering assistance. But, if she had rushed from the spot and met the murderer outside the library door, it would be simple enough to convey the impression that he had heard the shot, and that he was either dashing to their help, or making for the garden in the attempt to catch the villain red handed. The rifle was the only thing likely to provoke an awkward question, but he could have dropped it in the dark and returned for it afterwards without much fear of detection. As it happened, he thought it safer to risk carrying it indoors, and hid it under the billiard-room sofa till he had a chance to clean it and take it to the gun-room, as we now know.