After his conviction, Hannan was detained at the Auckland Prison in Paremoremo, where he worked at the prison quarry. Aside from a short-lived prison escape in the mid-1950s, he remained there until his eventual cancer diagnosis in 1962. Around June of that year, he contacted his former lawyer, George Israel Joseph, and gave details to the previous three murders. After his passing, Joseph wrote a book about unsolved murders in 1982, in which he wrote down the confessions in great detail, but referred to Hannan simply by "X". A few years after the book's publication, a policeman by the name of Sherwood Young read it and contacted Joseph to ask about the client's name, with the latter revealing him to be Hannan. Subsequently, Young revealed all of this information after writing a biographical article on Annie Smyth's life, noting that it was highly unlikely that any comparisons of Hannan's fingerprints and that of those found at the crime scene had been done.
