Detectives will now look again at three mysterious deaths linked to Cooper.
Cooper was befriended by kind hearted neighbour Florence "Flo" Evans, a pensioner who lived at Thornhill, Jordanston.
She took a liking to Cooper and tried to find some land for him to buy to establish a smallholding, in the hope that he and his wife Patricia would stay in the area. Both ended up dead.
Just days after complaining to friends that she couldn't find her house keys Flo Evans was found fully clothed and drowned in her bath. It was 1989--the same year Cooper blasted to death Peter and Gwenda Dixon.
Cooper had a habit of stealing house keys--police found 503 in a cess pit at his home.
Flo Evans' death was put down to her slipping into the bath and banging her head.
But it is now known that Cooper regularly burgled the homes of people he knew and reacted violently if disturbed.
Detectives believe that when he broke into Scoveston Park he thought the Thomases were out. On being seen by Helen Thomas he tied her up, blindfolded and gagged her.
When her brother arrived home he fired a long distance shot from a double barrelled 12 bore shotgun, wounding him in the head.
He then chased Mr Thomas into an outhouse and shot him in the stomach with the barrel so close it was actually touching him.
Cooper then dragged his lifeless body inside the house and set it on fire, having first returned upstairs and shot Helen Thomas.
Cooper had worked for the Thomases both at Scoveston Park and Norton Farm, which they also owned.
Detectives will also re-examine the deaths of retired farmer Griff Thomas and his sister Martha, who died in almost identical circumstances.
They were found shot to death in their burning farmhouse at Ffynnon Samson in the village of Llangolman, a few miles from where Cooper lived.
Cooper had been working in the area at the time fixing fences.
A coroner returned verdicts of manslaughter on Mrs Thomas, aged 70, and an open verdict for her 73 year old brother.
That was the initial theory about what had happened at Scoveston Park--until a pathologist told detectives Richard Thomas had been shot twice.
"We've got to look at these deaths again," said a detective who helped bring Cooper to justice.
"If Flo Evans came across Cooper as he burgled her house he would have done something about it. She knew him well and would have recognised him.
"And the circumstances at Ffynnon Samson are identical to Scoveston Park."
Cooper was notorious in the area for his violence. He rented a house at St Mary's Park, Jordanston, beat up the owner Mike Richards and never paid rent for the next eight years.
He also attacked his own son, Adrian, who left home as soon as he could and changed his name to Andrew.
Cooper changed after winning £94,000 in 1980 in a newspaper's spot the ball competition.
He began to gamble heavily and the money was soon gone. By 1983 he was breaking into properties he could reach on foot by crossing fields in the dark. He clipped paths through hedges that enabled him to apparently walk--or run if he had to--straight through.
Cooper was desperate to get back his rich lifestyle and in 1989 appeared on ITV's Bullseye programme, but left empty handed.
Just a few days after the episode was filmed he shot dead the Dixons for a "pitiful" amount of cash. He even stole Peter Dixon's wedding ring and sold it for £25, and took his wife's shorts as a trophy.
He was finally stopped after retired teacher Sheila Clark put up a fight after he broke into her house in the village of Sardis in 1996. She was expecting her husband to arrive and as she poured him a glass of red wine Cooper burst into the lounge.
He beat her with a shotgun, gagged her and tied her up. But Mrs Clark managed to wriggle free and press a panic alarm.
For once Cooper panicked. He ran from the house and across fields to his own home.
The next day police were able to follow a trail of discarded items--including a shotgun (later found to have Peter Dixon's blood on it), a balaclava, gloves and jewellery belonging to Mrs Clark.
The trail led to Cooper's front door. He cooly told police his dog had been disturbed during the night and it must have been the robber running past.
But he was now at the top of the list of suspects.
During that investigation--Operation Huntsman--police recovered all the evidence they needed to convict Cooper of murder as well as the burglaries. But scientists had yet to develop the techniques that would eventually reveal the proof.