“That will be sufficient for our purpose,” he said. “Now let us compare the two sets of footprints—the ones we have just made, and the previous ones. Examine them for yourself, Marsland, and tell me if you can see any difference.”
Marsland did so. With the mystified air of a man performing a task he did not understand, he first scrutinized the footprints they had made while walking forwards, and then examined the backward ones.
“Find any difference in them?” asked Crewe.
Marsland stood up and straightened his back with the self-conscious look of an Englishman who feels he has been made to do something ridiculous.
“I cannot say that I do. They look very much alike to me.”
“You are not very observant,” said Crewe, with a smile. “Let me explain the difference. In ordinary walking a man puts down the heel of his boot first, and then, as he brings his body forward, he completes the impression of his foot. He lifts his heel first and springs off the ball of his foot for the next step. But in walking backwards a man puts down the ball of his foot first and makes but a very faint impression with his heel. If he walks very carefully because he is not sure of the ground, or because it is dark, he may take four or five steps without bringing his heel to the ground. If you compare the impressions your boots have made in the sand when we were walking forward with the others made by walking backward, you will find that few of the latter marks give the complete impression of your boot.”
“Yes, I see now,” said Marsland. “The difference is quite distinct.”
“When I examined the window this afternoon, and came to the conclusion that it had been forced from the inside, I felt certain that a murderer who had adopted such a trick in order to mislead the police would carry it out in every detail,” said Crewe. “After forcing the window he would get out of it in order to leave footprints underneath the window in the earth outside, and of course he would walk backwards from the window, in order to convey the impression that he had walked up to the window through the garden, forced it and then got into the house. As I expected, I found the footsteps leading away from the window were deep in the toe, with hardly any heel marks. It was as plain as daylight that the man who had made them had walked backwards from the window. But even if I had not been quite sure of this from the footprints themselves, there was additional confirmation. The backward footsteps led straight to a fruit tree about twenty feet from the window, and on examining that tree I found a small branch—a twig—had been broken and bent just where the footsteps were lost in the gravel walk. The man who got out of the window had bumped into the tree. Walking backwards he could neither see nor feel where he was going.”
“I see—I see,” Marsland stood silent for a moment evidently pondering deeply over Crewe’s chain of deductions. “It seems to me,” he said at length, “that this man, clever as he was, owed a great deal to accident.”
“In what respect?”