Evil John Cooper killed his first victims, brother and sister Helen and Richard Thomas, at their manor house near Milford Haven in 1985.
Four years later, he murdered Peter and Gwenda Dixon on a coastal path near Pembroke. But when Detective Superintendent Wilkins took over the serious crime unit at the Dyfed-Powys police force in 2006 the murders were still unsolved - despite years of hard work from a determined team of detectives.
While they knew Cooper could be behind the chilling crimes, they didn't have the evidence they needed to lock him up and it was a fight against time before he killed again.
And then, after more years of searching, they spotted something - a trophy Cooper stole from one of his victims which proved to be the
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