“If you look into criminology, you’ll find that the murderer for money reasons is a fairly definite type. He’s usually clever enough to devise a fresh method of murder, or of disposing of the body. Apart from that, he’s not a very brainy type. And he has a terrible knack of repeating the same method in successive crimes. Suppose you have to cross a boiling torrent by stepping from stone to stone. You get across the first time in safety. If you have to cross again, you’ll choose the same stones as before. You’ve proved them to be safe. Any other stones may be insecure and may bring you down. Now that’s the state of mind of the mass-murderer when he goes in for his work. He carries out his first crime by a novel method. He isn’t detected. So when he tries his hand again he follows his first procedure slavishly in all its mean details. These are the safe stepping-stones for him. Look at the case of Smith, how he repeated all the minutiæ of his bath-business time after time. Deeming used to put down a fresh cement floor in a room to cover the bodies of his victims. He did that more than once. He’d found it safe the first time, you see. If you read up Burke and Hare’s doings, you’ll find them a steady repetition of the same method applied without variation. It’s the mark of the mass-murderer. “So naturally, I expected the poisoned darts and the air-gun to come into play again, if Ernest carried his work to a further stage. And I made up my mind that I’d choose his next victim for him. He made two deadly slips in that interview he had with us, Wendover. Perhaps you noticed them?” Wendover shook his head. “You told me after our talk with him that I ought to know who the murderer was; but I didn’t guess it. What slips did he make?” “The first slip was when he volunteered that he had a bicycle and had used it to get down to the Maze. Once I had information that he owned a bicycle, his alibi with the sore toe disappeared instanter from my mind. His second slip was a worse one. He said to us that he hadn’t been down to the Maze since the murders. And then he let out that he knew the position of the loophole through which Roger Shandon was shot. Speaking of his mythical assailant he said: ‘He was at the same loophole as he’d used when he killed Roger.’ If he’d never been near the Maze, how could he have known where that loophole was? Perhaps you think he might have picked up the information from those who were there. But if he had, I doubt if he’d have phrased the thing as he did. He seemed to me to pitch on that description of its position simply because it was the easiest that came to hand—which meant that it conveyed something definite to his own mind.