Manuel was tried for these murders in a sensational trial at the Glasgow High Court. In a move that astounded many present, he sacked his lawyers and conducted his defence by himself. At one point, William Watt was called as a witness. Recently injured in a road accident, he appeared on a stretcher. Although the judge, Lord Cameron, admitted that Manuel conducted his defence "with a skill that is quite remarkable", the killer was unable to convince the jury of his innocence and he was found guilty of all charges against him, except for that of murdering Anne Kneilands, which had been dropped due to lack of evidence. His defence in relation to the Smart killings contained some highly implausible claims, e.g. that Peter Smart had gone on a spree and killed his family and then himself, and that Peter Smart had been a friend of his who had given him keys to the Smart house. On 11 July 1958, Manuel was hanged on the gallows at Barlinnie Prison by Harry Allen. His last words are reported to have been: "Turn up the radio and I'll go quietly".