Game show answer that exposed killer
The brutal double murders at a picturesque Welsh holiday spot shocked the UK in 1985.
Three days before Christmas, the charred remains of siblings Richard and Helen Thomas were found in the ruins of their remote Pembrokeshire farmhouse, Scoveston Manor.
Four years later, husband and wife Peter and Gwenda Dixon were murdered as they walked along the Pembrokeshire Coastal Path.
Their bodies were later found hidden in undergrowth, The Sun reports.
All four victims had been shot at point-blank range and it was clear the cases were linked.
Yet despite a huge police investigation, the killer remained at large for 20 years.
Then in a cold-case review that began in 2005 the case was finally cracked, thanks to advances in forensic science - and a vital clue in murderer John Cooper's appearance on TV game show Bullseye near the time of the second murders.
On the show Cooper told host Jim Bowen how he loved living in the area, and even mentioned the spot where the Dixons would later die.
TWO DOUBLE MURDERS
Now the story of how police finally tracked down the murderer, a former farm labourer dubbed the "Bullseye Killer" - is being told in a new ITV true-crime drama, The Pembrokeshire Murders.
The gripping three-part series is based on a book, The Pembrokeshire Murders: Catching The Bullseye Killer, by Steve Wilkins, the senior investigating officer in the case.
Steve, now 61, is played by Welsh-born Hollywood actor Luke Evans.
He grew up in the area and told The Sun: "Pembrokeshire was one of the safest places to live in the UK, with one of the lowest crime rates.
"So having two double murders was really the elephant in the room, and geographically they were so close together there was a strong possibility they were linked."
In the 1985 Thomas killings, millionaire farmer Richard, 58, and his 54-year-old sister Helen were murdered at their manor house near the village of Scoveston.
They were bound and gagged before Cooper shot them and set fire to the first floor of the remote farmhouse.
Then in June 1989, Peter Dixon, 51, and his wife Gwenda, 52, from Oxfordshire, were on the final day of their summer holiday when they were butchered on a footpath near the coastal village of Little Haven.
Gwenda was naked from the waist down and appeared to have been sexually assaulted.
Peter's hands had been tied behind his back. His 22-carat wedding ring and his wallet were stolen.
Artists' impressions of a "scruffy", bushy-haired man were drawn up using witness descriptions after Cooper was seen acting suspiciously near cashpoints in Haverfordwest and Pembroke, where the victim's bank card was used.
Officers later discovered the murder weapon was the same Belgian-made 12-bore shotgun that had belonged to Richard Thomas.
Later, in March 1996, a man wearing a balaclava and brandishing a sawn-off shotgun approached five teenagers in a field in nearby Milford Haven.
He raped a 16-year-old girl at knifepoint before indecently assaulting a 15-year-old girl.
The trail had long gone cold when Steve, a detective chief superintendent and head of crime operations for Dyfed-Powys Police, reopened the cases.
At the time, Cooper was already in jail, serving 16 years for 30 burglaries including robbing a woman with a sawn-off shotgun at her home in the village of Sardis.
Cooper, played by Keith Allen in the new drama, had become a prolific burglar after winning the equivalent of nearly half a million pounds in a spot-the-ball competition in 1978, then frittering it away on luxury holidays and a gambling habit.
While investigating his spate of break-ins, police had quizzed Cooper over the four murders. But he refused to talk and there was no forensic evidence to link him to the killings.
Steve and his team spent two years painstakingly going over all the material from the investigations.
He also hired leading criminal psychologist Dr Adrian West to build up a profile of the killer.
He recalled: "I asked Adrian, 'How dangerous is this guy?' and he said, 'Steve, I have only come across two people in my professional life who if I found in my bedroom in the middle of the night, I know I would have to kill them to survive.
"One is Donald Neilson, the so-called Black Panther, and the other is John Cooper'. And I just went cold. I just thought, 'Yes, this is a dangerous guy'."
The reopened investigation, codenamed Operation Ottawa, was top secret, and Steve wanted to keep it that way.
He explained: "That was because when I did go live with it, I wanted to control it so that Cooper was watching the TV while I was doing it. I wanted to see what impact it had on him."
But the officer's plans were almost scuppered when ITV journalist Jonathan Hill revealed his plan to make a news program reinvestigating the two double murders.
So they struck a deal - if Jonathan held off from making a program, in return he would get the exclusive about the case being reopened.
In November 2007, Steve revealed live on ITV Wales News that he was carrying out a cold-case review and made a renewed public appeal for witnesses.
Around three years into the investigation, he had yet to get the forensic breakthrough he needed.
Scientists had started examining a selection of the recovered items, including a double-barrelled sawn-off shotgun, balaclava and gloves found in hedgerows near the home of one of Cooper's robbery victims.
Then finally, forensic testing on a pair of shorts belonging to Cooper gave Steve the "golden nugget" he desperately needed.
He said: "The shorts we recovered were shorter than the ones in one of the artist's impressions. I asked the forensic experts to unpick the hem.
"What had happened was Cooper's wife, who was a seamstress, had shortened the shorts and in doing so she had actually sealed in some of the forensic evidence. They had found a minute stain on the shorts, tested it and it was Peter Dixon's blood.
"It was just overwhelming. Suddenly after all these years, you have now got a piece of forensic evidence which ties Cooper to two double murders.
"It was like a pack of cards falling over once we got that first golden nugget. From then, we were getting forensic hits virtually daily."
The next significant item was the shotgun found near the scene of the robbery in Sardis.
Steve said: "It had already been tested but there was paint on the barrel, so I asked them to take the paint off and look underneath.
"Cooper had handpainted it with black paint and in doing so had sealed in the blood of Peter Dixon.
"So not only did we have shorts taken from his house, we also had the murder weapon as well. It was just one of those moments that will stay with me for the rest of my life.
"Those shorts were forensically linked to two double murders, a rape and five robberies."
And with the help of journalist Jonathan, Steve also tracked down footage of Cooper appearing on Bullseye in the same year as the Dixons were murdered.
He said: "We always knew Cooper had been on Bullseye but what we didn't know was when it was filmed.
"The reason the footage was significant was because it was too long after the offence to be thinking of putting people on identification parades and things like that because he had changed so much.
"I needed to find a photograph of him taken at around the time of the murders to compare with the artist's impression of the possible offender.
"Jonathan spoke to someone at ITV and traced the episode. It was filmed less than four weeks before Cooper had murdered the Dixons.
"He managed just to bounce it frame by frame until they got him virtually in exactly the same position as the artist's impression.
"Jonathan sent it to me and I have never in my 33 years in the police seen such a close resemblance between an offender and an artist's impression. It's like a tracing."
Cooper had been released from prison on parole in January 2009.
Four months later, he was arrested over the four murders, a serious sexual assault and five attempted robberies in Milford Haven in 1996.
Steve said: "When we arrested him we found a map, gloves and a rope in the boot of his car.
"He was already starting to prepare. He had started gambling. He was already entering that spiral."
Cooper was charged and remanded in custody before his case was brought to trial at Swansea Crown Court in March 2011, and after an eight-week trial he was convicted of all charges and jailed for life.
For the new drama, Steve was on the set for much of the filming and said of the final courtroom scene: "It made the hairs on the back of my neck stand up. It was amazing the way Keith Allen played Cooper.
"He really captured the violent nature of him. He's so menacing. It sends a shiver down your spine."
Father-of-two Steve, who now lives in Cheshire with his second wife Diane, 56, added: "In the drama, there's a picture frame seen on the wall in my office.
"It says, 'There is no greater responsibility than for a fellow human being to investigate the circumstances of death of another human being'.
"And I actually did have that. When I used to brief my teams on murder inquiries, I always used to start off by saying that to them.
"We were representing the victims of the families so you have got to make sure you've got the right people.
"Believe it or not, I was never in any doubt that we would find the killer."
This post originally appeared on The Sun and has been republished with permission
Originally published as Game show answer that exposed killer