"He got that letter a little after five in the afternoon. He left me here, in this room, with Sloane and Webster, and was gone three-quarters of an hour. That was just before dinner. He had the second floor, on that side of the house, entirely to himself. He took a nail-file from Webster's dressing case, and in Webster's room put a sharper point on it by filing it roughly with the file-blade of his own pen knife.
"That's doubly proved: first, my magnet, with which I went over the floor in Webster's room, picked up small particles of steel. Here they are."
He produced a small packet and, without unwrapping it, handed it to Crown.
"Again: you'll find that the file-blade of his knife retained particles of the steel in the little furrows of its corrugated surface. I know, because last Sunday, as your car came up the driveway, I borrowed his knife, on the pretext of tightening a screw in the blade of mine. And I examined it."
He put up a silencing hand as Wilton forced a jeering laugh.
"But there's more to prove his manufacture and ownership of the weapon that killed the woman. He made the handle from the end of a slat on the bed in the room which I occupied that night. The inference is obvious: he didn't care to risk going outside the house to hunt for the wood he needed; he wouldn't take it from an easily visible place; and, having stolen something from one room, he paid his attention to mine. All this is the supercaution of the so-called 'smart criminal.' It matches the risk he took in returning to the body to hunt for the weapon. That was why he was there when Webster found the body.
"The handle of the dagger matches the wood of the slat I've just mentioned. You won't find that particular slat upstairs now. It was taken out of the house the next day, broken into sections and packed in his bag of golf-sticks. But there is proof in this room of the fact that he and he only made the dagger.
"You'll find in the edge of the large blade of his penknife a nick, triangular in shape, which left an unmistakable groove in the wood every time he cut into it. That little groove shows, to the naked eye, on the end of the shortened slat and on the handle of the dagger. If you doubt it——"
"Thunder!" Crown interrupted, in an awed tone. "You're right!"
He had taken the dagger from his pocket and given it minute scrutiny. He handed it now to Sloane.