Pembrokeshire murders killer John Cooper kept 500 sets of house keys hidden in a cess pit as sick trophies from his perverted crimes
The monster, who is now serving life for two double murders in Pembrokeshire in the 1980s, had started his life of crime as a burglar and peeping tom before he first killed.
Cooper took the lives of brother and sister Helen and Richard Thomas at their manor house near Milford Haven in 1985, and murdered husband and wife Peter and Gwenda Dixon on a coastal path near Pembroke in 1989.
The Mirror reports that the cop who cracked the case, retired Detective Superintendent Steve Wilkins, of Dyfed Powys police, set about investigating Cooper when he was already in prison serving a 14-year term for a string of violent burglaries in Pembrokeshire.
Mr Wilkins, 61, explained: “If you look at his history here is a guy that started off as a prolific dwelling house burglar and his MO was always the same.
“He lived in a rural area surrounded by fields and he used to prowl those fields at night, he knew the hedge rows and the night time landmarks.
“He used to cut fences in a way that would help him if he had to make an escape.
“He is a planner but he started out as a peeping tom, he would always attack females after in houses backing on to fields.
“After that he progresses to burglary realising he can steal items and cash he can use to fund his addictive gambling.
“He then starts to get confronted by homeowners so progresses to robbery and that control and the disproportionate violence would sexually arouse him and then we get to the sexual element of his crimes. So there was a clear progression.”
Chillingly Mr Wilkins revealed that Cooper enjoyed nothing more than taking a memento from his victims.
He said: “He also kept mementos, so when they searched his house they found 500 sets of keys in the cess pit.
“A lot of the property he stole was worthless but he kept it in the house anyway as trophy.
“The shorts which had the DNA on which led to his conviction, we found out he stole them from Gwenda Dixon when he murdered her.
“So he kept these mementos of his crime which would put him back into the time of the offence and let him re-live that control.”
Mr Wilkins also offered an insight into Cooper’s psyche and how control was the centre of everything he did.
He said: “Cooper is a guy who had a very inflated opinion of himself.
“For example thought of himself as businessman after winning £98,000 in a spot-the-ball competition which we would work out at about £300,000 in today’s money.
“And he suddenly decides, ‘we’re going to be Turkey farmers’ with no experience whatsoever and it fails straight away.
“He then decides to get into horse racing so buys a race horse for about £2,000 but brings it back on the motorway in a cheap horsebox with a rotten floor.
“So the poor horse falls through the floor on the motorway and breaks its legs and another business fails.
“He very quickly frittered his winnings away but when asked about it in interview it was always somebody else’s fault so his pattern was always the same.
“He had an over inflated view of his abilities and when his plans failed it was never his fault.”
The dramatic investigation, which took in evidence from beyond the grave as well as the appearance by Cooper on popular TV quiz show Bullseye, was made into a three-part drama starring Luke Evans and Keith Allen which aired on ITV this week raking in millions of viewers.