“I should say never,” Trent replied; “and the reason is, that even the cleverest criminals seldom run to strategic subtlety. When they do, they don’t get caught, since clever policemen have if possible less strategic subtlety than the ordinary clever criminal. But that rather deep quality seems very rarely to go with the criminal make-up. Look at Crippen. He was a very clever criminal as they go. He solved the central problem of every clandestine murder, the disposal of the body, with extreme neatness. But how far did he see through the game? The criminal and the policeman are often swift and bold tacticians, but neither of them is good for more than a quite simple plan. After all, it’s a rare faculty in any walk of life.” “One disturbing reflection was left on my mind,” said Mr. Cupples, who seemed to have had enough of abstractions for the moment, “by what we learned today. If Marlowe had suspected nothing and walked into the trap, he would almost certainly have been hanged. Now how often may not a plan to throw the guilt of murder on an innocent person have been practised successfully? There are, I imagine, numbers of cases in which the accused, being found guilty on circumstantial evidence, have died protesting their innocence. I shall never approve again of a death-sentence imposed in a case decided upon such evidence.” “I never have done so, for my part,” said Trent. “To hang in such cases seems to me flying in the face of the perfectly obvious and sound principle expressed in the saying that ‘you never can tell’. I agree with the American jurist who lays it down that we should not hang a yellow dog for stealing jam on circumstantial evidence, not even if he has jam all over his nose. As for attempts being made by malevolent persons to fix crimes upon innocent men, of course it is constantly happening. It’s a marked feature, for instance, of all systems of rule by coercion, whether in Ireland or Russia or India or Korea; if the police cannot get hold of a man they think dangerous by fair means, they do it by foul. But there’s one case in the State Trials that is peculiarly to the point, because not only was it a case of fastening a murder on innocent people, but the plotter did in effect what Manderson did; he gave up his own life in order to secure the death of his victims. Probably you have heard of the Campden Case.” Mr. Cupples confessed his ignorance and took another potato.