The jury without hesitation found Courvoisier guilty, and he was sentenced to death. The prisoner's demeanour had greatly changed during the trial. Coolness amounting almost to effrontery gave way to hopeless dejection. On his removal to Newgate after sentence, he admitted that he had been justly convicted, and expressed great anxiety that his fellow-servants should be relieved from all suspicion. Later in the day he tried to commit suicide by cramming a towel down his throat, but was prevented. Next morning he made a full confession in presence of his attorney, and the governor, Mr. Cope. In this he gave as the motives of his crime a quarrel he had with his master, who threatened to discharge him without a character. Lord William, according to the valet, was of a peevish, difficult temper; he was annoyed with his man for various small omissions and acts of forgetfulness, and on the night of the murder had taken Courvoisier to task rather sharply. Finally, on coming downstairs after bed-time, Lord William had found Courvoisier in the dining-room. "What are you doing here?" asked his lordship. "You can have no good intentions; you must quit my service to-morrow morning." This seems to have decided Courvoisier, who took a carving-knife from the sideboard in the dining-room, went upstairs to Lord William's bed-room, and drew the knife across his throat. "He appeared to die instantly," said the murderer, in conclusion. His account of his acts and movements after the deed varied so considerably in the several documents he left behind, that too much reliance cannot be placed upon his confession. His last statement contains the words, "The public now think I am a liar, and they will not believe me when I say the truth." This was no doubt the case, but this much truth his confession may be taken to contain: that Courvoisier was idle, discontented, ready to take offence, greedy of gain; that he could not resist the opportunity for robbery offered him by his situation at Lord William Russell's; that when vexed with his master he did not shrink from murder, both for revenge and to conceal his other crimes.
Courvoisier wished to commit suicide in Newgate, but was prevented by the vigilant supervision to which he was subjected while in gaol. The attempt was to have been made by opening a vein and allowing himself to bleed to death. The Sunday night before his execution he would not go to bed when ordered. The governor insisted, but Courvoisier showed great reluctance to strip. The order was, however, at length obeyed, and the whole of the prisoner's clothes were minutely searched. In the pocket of the coat Mr. Cope, the governor, found a neatly-folded cloth, and asked what it was for. Courvoisier admitted that he had intended to bind it tightly round his arm and bleed himself to death in the night. The next inquiry was how he hoped to open a vein. "With a bit of sharpened stick picked out of the ordinary firewood." "Where is it?" asked the governor. The prisoner replied that he had left it in the mattress of which he had just been deprived. The bed was searched, but no piece of sharpened wood was found. It was thought that it might have been lost in changing the mattresses. The cloth above referred to belonged to the inner seam of his trousers, which he had managed to tear out. There is nothing to show that Courvoisier really contemplated self-destruction.