In this episode, Ian Rankin explains that by the dawn of the 80s, the only hope of catching the World’s End killers lay with the people developing new techniques in forensic science. Astonishing archive footage reveals how policing underwent a revolution throughout the decade, fuelled by advances in forensic science, DNA fingerprinting and information technology. The programme also reveals how the FBI’s pioneering advances in forensic psychology led to hopes that psychological profiles of the World’s End killers could be created. Retired DCC Tom Wood reveals that he travelled to the FBI's headquarters with files on the unsolved murders from the late 70s in search of answers.