There was "an extremely strong possibility" that a tiny screw found at the home of farm labourer John William Cooper came from a gun used in a double murder, a jury heard today.

The double barrelled shotgun, argued Gerard Elias QC, prosecuting, was thrown away by Cooper as he fled from a robbery at a house in Sardis in 1996.

Cooper was later convicted of the robbery in 1998 and jailed for 10 years, plus an additional six years for 30 burglaries.

Thousands of items found at Cooper's home were retained by police, including the gun. As DNA techniques advanced scientists retested the shot gun "and there is no doubt" that they found, underneath black paint on one of the barrels, the blood of holidaymaker Peter Dixon, said Mr Elias.

Mr Dixon, 51, and his wife Gwenda, aged 52, were tied up and shot dead as they walked the Pembrokeshire Coastal Path in 1989.

Ian Johnson, a forensic scientist and gun expert, told Swansea crown court today he examined the shotgun and a screw found by detectives at Cooper's then home in St Mary's Park, Jordanston.

He said there was a screw missing from the weapon and there was "an extremely strong possibility" it was the one found by police.

Mr Johnson said the single screw and the ones still in the gun bore distinctive markings.

He said several changes had been made to the weapon and both the stock and the barrels had been shortened.

Cooper was jailed in 1998 as a result of Operation Huntsman, said Mr Elias, even though he denied all the charges against him.

During Operation Huntsman detectives found thousands of items both at his home and hidden in hedgerows nearby. Now, added Mr Elias, scientists could link several of the items with the scenes of crimes.

They include the murders of brother and sister Richard and Helen Thomas, who were shot dead at their home, Scoveston Park, in 1985.

And gloves would also link Cooper to the rape of a 16 year-old girl in 1996, and the indecent assault of her friend, it was claimed.

Cooper, now of Spring Gardens, Letterston, denies four murders, rape, indecent assault and five charges of attempted robbery.

The trial continues.