Collaborations between journalists and criminals often end badly, with the former either being duped by the latter (as Norman Mailer was by Jack Henry Abbott) or “gaining their trust and betraying them without remorse” (Janet Malcolm’s description of Joe McGinniss’s treatment of the murderer Jeffrey MacDonald in his book Fatal Vision). Machell’s book is an honourable exception. He has had considerable help from his subject (referred to throughout as Stephen) without surrendering editorial freedom or fully buying into his version of events. Drawing heavily on Jackley’s journals and diligently tracking down people who met him at different points of his life, the book explains but doesn’t exonerate...