In this episode, Ian Rankin explains that by the dawn of the 80s, the only hope for 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 HQ with files on the unsolved murders from the late 70s in search of answers.
In the late 80s, advances in DNA fingerprinting technology also brought hope to the detectives on the case. Some biological evidence had been discovered on Helen Scott's coat, and forensic scientists succeeded in using it to obtain a clear DNA profile. However, when they tried to match it with existing DNA profiles held on police records across the UK, no match could be found.Through the 90s, further advances in forensic science meant that DNA analysis became both more sensitive and more effective. A reanalysis of the stain on Helen's coat revealed that there was more than one person's DNA present. This second sample was examined and matched to notorious sexual offender Angus Sinclair, who was serving two life-sentences in Peterhead Prison.Investigators then desperately try and discover which other murders might have been committed by Sinclair, and this episode reveals how the first trial against Sinclair would go on to controversially collapse. It would take a change of law and a new advance in forensic science to see him finally brought to justice.