The detective who helped catch the serial killer behind the Pembrokeshire Murders has said the diagnosed psychopath behind the crimes was the 'most dangerous human being'.
John Cooper, now 76, was finally brought to justice in 2011 when he was jailed for life for two brutal double murders from two decades earlier.
Siblings Richard and Helen Thomas were found dead at their farmhouse in Wales in 1985, and the bodies of Peter and Gwenda Dixon were discovered by the Pembrokeshire coastal path four years later.
In 2006, Detective Superintendent Steve Wilkins led a review of the then unsolved double murder cases - which was portrayed in the true crime drama The Pembrokeshire Murders this week - and soon found enough evidence against Cooper.
Speaking on ITV's The Pembrokeshire Murders: Catching The Game Show Killer, which airs tonight at 9pm, DS Wilkins admitted that Cooper found murdering somebody for property 'totally justifiable' and would have 'no doubt killed again'.
The detective (pictured, Detective Superintendent Steve Wilkins) who helped catch the serial killer behind the Pembrokeshire Murders has said the diagnosed psychopath behind the crimes was the 'most dangerous human being'
John Cooper (pictured), now 76, was finally brought to justice in 2011 when he was jailed for life for two brutal double murders from two decades earlier
'He is the most dangerous human being that I’ve ever come into contact with,' said DS Wilkins. 'This was about excessive violence - and for him, taking somebody’s life in order to take property off them is totally justifiable.'
'I was in no doubt that Cooper would kill again,' said the detective, who led the review case, called the Operation Ottawa.
Despite having more than a million documents to review, DS Wilkins was confident they would catch the serial killer and re-examined the items from Cooper's home.
'From day one, I felt that we would find the person responsible, that we would find the truth. Evidence is always there, you've just got to find it.'
Detectives were able to nail Cooper for the murders through advancements in DNA testing, as well as linking him to the area where the crimes were committed after comments he made while appearing on the game show Bullseye.
In 2006, Detective Superintendent Steve Wilkins led a review of the then unsolved double murder cases - which was portrayed in the true crime drama The Pembrokeshire Murders this week - and soon found enough evidence against Cooper (pictured)
On the show, the murderer bragged about his extensive geographical knowledge of the Pembrokeshire coastline upon which the Dixons were later killed.
The unearthed footage of Cooper on Bullseye also showed him looking remarkably similar to a police sketch of the killer from a witness' description following the Dixons' deaths.
DS Wilkins said: 'It was unbelievable, in my 33 years in the police I have never seen a comparison between an artist's impression and that of a suspect - it was like a tracing.'
Evidence against Cooper also included blood from one of the victims discovered in the hem of the serial killer’s shorts after it had been sewn up to hide the stain.
Cooper's long history of crimes already included 30 robberies and a violent assault - for which he was arrested and sentenced to 14 years in 1998 for burglary and robbery before being released in 2009.
A breakthrough came for DS Wilkins in 2009 when unearthed footage of Cooper on Bullseye (pictured left) showed him looking remarkably similar to a police sketch (pictured right) of the killer from a witness' description following the Dixons' deaths
'He was about to be released on parole and I'd got no doubt he'd start his offending again. I knew they'd only be one end to that. Cooper would kill again,' said DS Wilkins on tonight's programme.
Eventually, using advanced developments in DNA and scientific evidence, detectives were able to link the gun used in a robbery Cooper was convicted of to the murder weapon in the Dixon's case.
Several items belonging to both sets of victims were also found in his possession.
Although Cooper denied his guilt, he was arrested and convicted of two double murders and jailed for life in May 2011 for the two double murders.
After an eight-week trial the serial killer was also convicted of separate offences of rape, sexual assault, and attempted robbery - he will never be released.
The Pembrokeshire Murders: Catching The Game Show Killer ITV 9pm tonight
