As Peter Tobin faces sentencing for the murder of Dinah McNicol, Mark Austin speaks to criminologists, psychologists and those who have come face-to-face with the man to deduce whether Tobin is Britain's worst serial killer. The programme examines Tobin's past to see what drove the man to become a monster, talking to his two ex-wives and the women he befriended in the months before he killed Angelika Kluk. It also explores the first crime he was convicted of - the double rape of two young girls in 1993.

• Mark Austin