A farm labourer "mercilessly executed" four people in return for pitifully small amounts of money, a jury heard today (Tuesday).

John William Cooper, now 66, blasted them to death with a shotgun just to ensure his escape, said Gerard Elias QC.

And he probably decided not to shoot a group of teenagers he had attacked only because there were too many of them, he alleged.

But before leaving them "cowed and terrified" he fired the gun in the air and warned them he would murder them if they went to the police.

Cooper, of Spring Gardens, Letterston, denies murdering millionaire farmer Richard Thomas, 58, and his sister Helen, 56, at their home at Scoveston Park on December 22, 1985.

He also denies murdering marketing director Peter Dixon, 51, and his wife Gwenda, on June 29, 1989.

Cooper also denies raping one of the teenagers, indecently assaulting another and trying to rob the other three.

Mr Elias told Swansea crown court Cooper had been a prolific burglar and in December 1998 had been jailed for 16 years for 30 break ins and a robbery, all involving properties he could reach on foot from his then home in St Mary's Park.

While he served 10 years in jail a cold case review began to connect him to the crimes he is now accused of, it was alleged.

Mr Elias said a man with local knowledge had performed the murders and Cooper knew the area like the back of his hand.

The robbery for which he had been convicted in 1998 involved a man wearing a balaclava, gloves and armed with a sawn off shotgun - as had the man who attacked the teenagers on March 6, 1996.

The killings, said Mr Elias, involved "the use of cold, calculating violence and the merciless execution of four people for pitifully small financial gain but to ensure their silence.

"It might be the teenagers were spared because there were too many of them to be executed.

"They were put through a terrifying ordeal by a man prepared to hand out sickening violence, who had no compunction about ending the life of a victim if it increased his chances of escape.

"He is also devious and scheming and will stop at nothing to evade justice."

Mr Elias said the crimes were linked by "a large number of common threads that go way beyond the possibility of innocent coincidence."

And there were "many connections" between the earlier burglaries and robbery and the present charges faced by Cooper.

He said it was likely Cooper had targeted Scoveston Park, a large manor house with a courtyard and outbuildings, because he thought Helen Thomas would be alone.

But while he was robbing her Richard Thomas arrived. Cooper took him to an outbuilding and shot him and killed his sister "as his way out of being" identified, it was claimed.

Before he escaped, Cooper allegedly used diesel to fuel a fire and Scoveston Park burned to the ground.

Peter and Gwenda Dixon, from Oxfordshire, had spent two weeks walking the Pembrokeshire Coastal footpath and were on their last walk when they came across their killer.

Cooper, it was alleged, confronted them at gunpoint on a clifftop near Little Haven and forced them 20 yards off the path to a hideaway above a huge drop to the sea, that only a local man would have known about.

Having been tied up and robbed and forced to give their bank details, they were "silenced for all time" to give Cooper the chance to use the cards to extract cash, alleged the prosector.

The five teenagers, aged 15 and 16, were approached in a field by the Mount Estate, Milford Haven, and forced away from local housing. Cooper, it was alleged, was wearing a balaclava and gloves and brandished a sawn off shotgun.

He ordered them all to lie face down and then dragged a 16 year old girl away by her hair and raped her at knifepoint. He returned and indecently assaulted another girl "while the rest of the group cowed."

Before leaving he tried to rob them all. Then he warned them he knew who they were and "to reinforce his threat to kill them if they spoke" he fired the gun into the air.

Mr Elias said sexual gratification may have been one motive for the crimes. That was plain in the rape and indecent assault, but there was also evidence that Gwenda Dixon had been sexually assaulted either before or after she had been killed.

These "most serious of crimes" had all taken place in a tiny corner of south west Wales and each involved the use of cold and calculating violence.

The killer, said Mr Elias, was plainly a local man who knew his way around, and Cooper's home at the time "stood at the epicentre of these events." Cooper used to fish at Little Haven and got around the area on foot and by bicycle both during the day and at night.

During Cooper's burglary spree, which went on for more than 10 years before he was caught in early 1998, it emerged that he had cut wire fences so he could cross fields and "walk through" hedges when no-one else could see a route.

He had also used hedgerows, as others would use safes at home, to stash the proceeds of crimes knowing they would be far from his home but unlikely to be stumbled upon.

The trial continues.