This film tells the remarkable story of Wales' most dangerous serial killer.John Cooper terrorised the usually safe county of Pembrokeshire for more than a decade, committing two double murders, a violent robbery, rape and sexual assault of children and a spree of armed robberies and burglaries. He was so prolific that the crime rate dropped by 90% after his arrest.This film tells the story of Cooper's horrific crimes and how police finally brought him to justice. With access to original case materials and police interview videos with Cooper, it reveals how police launched a cold case review into unsolved crimes, and used forensic techniques to reach a breakthrough.John Cooper was a family man, and a local celebrity, who hid his crimes for over a decade. A ruthless killer, Cooper attacked and murdered holidaymakers and local landowners – and used extreme violence. For years the identity of the murderer remained a mystery, until police uncovered crucial forensic evidence. Twenty-four years after his first murders, John Cooper was given a whole life sentence, joining the list of 46 criminals told they will die behind bars.