The rape and murder of two Edinburgh teenagers from the World's End pub in 1977 sparked an nationwide manhunt that would last four decades. Convicted killer and child rapist Angus Sinclair was sensationally cleared of the murders in 2007. With 'double jeopardy' laws under review, BBC Scotland investigates whether he could ever take the stand again. Mark Daly secures unprecedented access to detectives, witnesses and video interviews with Sinclair, and reveals his criminal career.—BBC Scotland