Described by Mr Chandler as "a dark man with a moustache and a pipe", Mr Day-Hakker was a party guest at the Chatswood Party. He was the last guest to arrive, after 3am, and did so independently of his wife. He was late because he was working as a pianist in a Kings Cross nightclub.

Mr Day-Hakker had not met either Bogle or the Chandlers before he arrived at the party. Called to the Inquest on 8th May 1963, it was wondered what he might be called for, having not been present for most of the party. A possible explanation may be that his testimony, and that of his wife, differed so much from that of all the other party witnesses that it was considered proper, in the name of thoroughness, to present the opposite viewpoint.

Mr Day-Hakker and his wife were routinely interviewed early in the enquiry. On reflection, however, he felt that he had more information to give. His wife phoned police on 8th January 1963 to this effect. Detective Sergeant Harry Parsons, the first detective to arrive at Fuller's Bridge, visited immediately.

Mr Day-Hakker's statement to the police said that he'd engaged Dr Bogle and Miss Beavis in conversation. Bogle looked quite fit when Day-Hakker had first seen him. By 4:15am, however, "Dr Bogle was stooped over and looked sick and gave me the impression that he could not register a reply to this person and I got the impression that he was really sick and could not care less whether he saw anyone or not at that stage."

At the Inquest, Mr Day-Hakker explained that he'd since had cause to revise the statement, because he was not a very good judge of such things, and he'd only met Bogle that night.