Susanna Reid tells the story of the search for Pembrokeshire serial killer John Cooper, who murdered four people in Wales between 1985 and 1989, but avoided capture for more than 20 years - until the combination of a new detective team, advances in forensic science finally brought him to justice in 2011. His crimes began in 1985, when he shot a brother and sister at their farm near Milford Haven. Four years later, he killed a couple as they walked along a coastal path. However, it would be his 1989 appearance the TV game show Bullseye that would eventually prove his undoing