"How is that vital?" asked Walters, who was keenly interested in understanding how Crewe had arrived at his conviction of Kemp's guilt.
"Holymead's appointment with Sir Horace at Riversbrook was for 9.30 p.m. The letter found in Sir Horace's pocket-book fixed that time. It was exactly 11 p.m. when he got into a taxi at Hyde Park Corner after his visit to Riversbrook. On that point the driver of the taxi was absolutely certain. I was so anxious for him to make it 11.30 that I went to see him twice about it. Assuming that Holymead arrived at Riversbrook at 9.30, I allowed half an hour for his angry interview with Sir Horace, half an hour for the walk from Riversbrook to Hampstead Tube station, and half an hour for the journey from Hampstead to Hyde Park Corner, which would have involved a change at Leicester Square. As I could not induce the driver of the taxi to make Holymead's appearance at Hyde Park Corner 11.30 instead of 11, I had to admit that Holymead must have left Riversbrook at 10. But it was 10.30 according to Mademoiselle Chiron when she found Sir Horace dying on the floor of the library. Therefore if Holymead did the shooting, the victim's death agonies must have lasted half an hour or more. Medically that was not impossible, but somewhat improbable. But a meeting between Kemp and Sir Horace after Holymead had gone filled in the blank in time. That came home to me yesterday when Kemp was in the witness-box committing perjury in his determination to get Holymead off. I take it that the interview between Kemp and his victim lasted about 20 minutes. Therefore Sir Horace was shot about 10.20; certainly before 10.30, for Mademoiselle heard no shots while nearing the house."
"You have worked it out very ingeniously," said Walters. "You must find the work of crime detection very fascinating. I am afraid that if I had been in your place—that is if I had known as much about the tragedy as you do—when Kemp was in the witness-box yesterday, I would not have seen anything more in his evidence than the fact that he was committing perjury in order to help Holymead."
"I think you would," said Crewe. "These discoveries come to one naturally as the result of training one's mind in a particular direction."
"They come to you, but they wouldn't come to me," said Walters with a smile. "But do you think Kemp's story of how Sir Horace was shot is literally true? Do you think Sir Horace got in the first shot and then tried to fire again? If that is so, I don't see how they can hope to convict Kemp of murder—a jury would not go beyond a verdict of manslaughter in such a case."
"You handled Kemp so well that he was too excited to tell anything but the truth," said Crewe. "Sir Horace fired first and missed—the bullet which Chippenfield removed from the wall of the library shows that—and he pulled the trigger again but the cartridge which had been in the revolver for a considerable time, probably for years, missed fire. Here is a silent witness to the truth of that part of Kemp's story."
Crewe produced from a waistcoat pocket one of the four cartridges he had removed from the revolver Mademoiselle Chiron had handed to him and he placed it on the table. On the cap of the cartridge was a mark where the hammer had struck without exploding the powder.