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Twisted John Cooper believed he had got away with two double murders as he remained undetected for decades.
The evil killer murdered brother and sister Richard and Helen Thomas in 1985 with a shotgun, then torched their three-storey manor house near Milford Haven, Wales.
Four years later, Cooper even brazenly made an appearance on ITV gameshow Bullseye, then committed another sickening double murder exactly one month after.
He brutally killed hikers Peter and Gwenda Dixon on a coastal path in Pembrokeshire in 1989.
Despite the best efforts of the police, Cooper managed to evade the law for years and no-one was charged with the two murders.
However, the murderer was finally exposed by a crucial piece of evidence that Cooper had stolen from one of his victims as a sick trophy – and his wife was inadvertently responsible.
John Cooper (right) pictured with Bullseye host Jim Bowen on the show
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In 2006, DCI Steve Wilkins returned to Wales after a stint at Scotland Yard and began a new job as Deputy Head of Dyfed Powys CID.
Given the nationwide impact DNA forensic science was having on solve rates in serious crime, Steve decided to put a team together and reinvestigate the two double murders from the 80s.
Steve knew that a large number of exhibits from the original investigations into the murders were still in storage and hoped they would yield the crucial evidence he needed.
At the time, Cooper was serving a 14-year term for a string of violent burglaries in Pembrokeshire.
Steve was convinced that Cooper was responsible, but needed to find what he described as a ‘Golden Nugget’ of evidence before the criminal was let out on parole.
Former Detective Superintendent Steve Wilkins brought the killer to justice
(Image: Julian Hamilton/Daily Mirror)
It was Cooper's wife Pat, who put up with years of abuse at the hands of her cruel husband, who unknowingly provided the piece of evidence that brought him to justice.
A police sketch from 1989, known as the "wildman" sketch, depicted a "scruffy" bushy-haired man seen using Peter Dixon’s cash card at an ATM after his murder.
It was actually ITV journalist Jonathan Hill who found the archived footage of Cooper's appearance on Bullseye.
Put together, the clip from the show and artist's impression of the killer proved with stunning clarity that, shortly before the murders, Cooper had borne a striking resemblance to the only existing image of the murder.
"I couldn’t believe my eyes there was John Cooper as bold as brass," explained Jonathan.
But it was an item of clothing that would ultimately bring Cooper down.
The police sketch of the original suspect is shown on the right, who was described as a "scruffy" bushy-haired man, and bared a striking resemblance to Cooper on Bullseye (left)
After three-and-a-half years of meticulous police work, Wilkins could not believe they hadn't had a forensic hit.
But he eventually got his 'golden nugget' when a policewoman noticed some khaki shorts seized from Cooper bore a resemblance to those in the sketch, and also appeared to be women’s.
The shorts belonged to murder victim Gwenda Dixon and had been kept by Cooper as a sick trophy.
But his unsuspecting wife Pat turned them up – and in doing so trapped vital DNA evidence in the seams.
"We found the DNA of Peter Dixon’s daughter trapped in the seam," explained Wilkins.
Just four years after the first double murder he committed, Cooper ruthlessly killed Peter and Gwenda Dixon on a coastal path near Pembroke
"Now she’d been in Cyprus at the time of the murders so how the hell does her DNA make it into shorts owned by John Cooper unless they actually belonged to the Dixons?
"It’s absolutely incredible to think Pat’s simple act would lead to him finally facing justice."
It also tied Cooper to an attack on five teens in Pembrokeshire in 1996, who were confronted by a man in a balaclava brandishing a sawn-off shotgun who demanded cash and subjected two girls to serious sexual assaults.
"When they realised Cooper’s wife was a seamstress and there was this discrepancy between the long legged shorts and the short shorts, they thought maybe she had shortened them," said ITV journalist Jonathan Hill.
"Unbeknown to Pat Cooper, when she had rolled up the hem and stitched it, she had sealed in the blood evidence that would ultimately convict her husband."
John's wife Pat Cooper being played by Caroline Berry in the show
(Image: WORLD PRODUCTIONS/ITV)
Cooper was arrested in May 2009 after a lengthy investigation and forensic costs that were more than £1million over-budget.
In addition, a Swansea Crown Court jury further convicted Cooper of sticking up five terrified teenagers at gunpoint in woods on Milford Haven’s Mount Estate in 1996, where he raped one 16-year-old girl and indecently assaulted another, aged 15.
He was convicted of all charges and jailed for life in May 2011 – and remains in prison to this day at the age of 76.
But Pat had already passed away a few years before in devastating circumstances.
John Cooper who has been found guilty of the two double murders of Peter Dixon and Gwenda Dixon and Richard Thomas and Helen Thomas in Pembrokeshire, West Wales in 1985. In 1996 he also raped a teenage girl and assaulted her friend. New DNA evidence has secured his conviction today. © WALES NEWS SERVICE
(Image: Wales News Service)
During Cooper's first night of freedom after being released from prison in Christmas 2008, Pat died of a heart attack.
She is played by Caroline Berry, who has starred in Doctor Who, Doctors and most famously as killer Pat Phelan's wife in Coronation Street.
Executive Producer Simon Heath said: "Caroline Berry is brilliant as Cooper’s put-upon wife, Pat.
"She’s absolutely terrified of him, unable to escape the controlling influence Cooper exerts on her, even while he resides in prison.
"When Cooper is finally released, her terror is palpable and leads to tragedy."
John Cooper appeared on a Bullseye episode in May 1989, pictured alongside presenter Jim Bowen
Cooper's vile crimes are being revisited in new ITV drama series The Pembrokeshire Murders, where he is played by actor Keith Allen.
Keith will be de-aged to bring to life the disturbing scenes from the 80s when he appeared on Bullseye.
Cooper failed to answers enough general knowledge questions in the first round, then missed the target with all three of his darts in the final round.
Behind the smile he put on for the cameras, he was hiding a sickening killer secret.
It was only two decades later that the police realised he had been on the show – and their darkest theories were seemingly confirmed when ITV journalist Jonathan Hill matched up the footage with the artist's impression of the killer.
"Jonathan did some work with his team to freeze the Bullseye footage in the same position as the artist's impression," said Wilkins.
His appearance showed he had intimate knowledge of the area where the English hiking couple had been killed
"He sent it to me and I remember just looking at it and I can honestly say in my 33 years in the police when I’ve seen hundreds and hundred of artists' impressions.
"As a likeness, I’ve never seen one as close as this. It was one of those jaw dropping moments – I thought, ‘that’s him!"
In addition to his appearance, Cooper's discussion about his love of the great outdoors and lengthy details about the geography of the West Wales countryside aroused further suspicion.
It showed he had intimate knowledge of the area where the English hiking couple had been killed.
But it was DNA evidence that was the "golden nugget" that eventually brought Cooper down.
*The Pembrokeshire Murders airs tonight on ITV at 9pm