Advances in DNA forensics and computer technology have prompted Dyfed-Powys Police to re-open their investigations of two brutal unsolved double murders committed 18 and 22 years ago.

In "Operation Ottawa" top detectives have launched what they describe as "a thorough cold case thematic forensic review" in the hope of finally closing the files on the cold-blooded murders of siblings Richard and Helen Thomas at Scoveston Park, Steynton, in December 1985, and husband and wife Peter (51) and Gwenda (52) Dixon on the coastal path near Little Haven in July 1989.

All four died from close-range gunshot wounds, and the investigators were unable to establish either motives or perpetrators.

At a Press Conference at Haverfordwest on Thursday, Detective Chief Superintendent Steve Wilkinson, whon heads the review, said: "The Operation Ottawa team have been selected to provide a fresh and independent view of the enquiries and have been speaking to officers who were involved in the original investigations.

"For the past two years the team have gone through a painstaking process of recovering, cataloguing and recording all the relevant material.

"There has been considerable success Evidence in the Scoveston Park murders indicated that Helen Thomas had been attacked in her bed and that her brother Richard was shot on the stairs as he returned and disturbed the murderer or murderers, who then set the Georgian manorhouse ablaze to destroy the evidence.

In the Dixon case the unsuspecting couple were walking the coast path from their base at Howelston Caravan Park,Talbenny, when they were gunned down and their bodies concealed in undergrowth covering a steep cliff slope near Talbenny Church.

Two theories propounded at the time were that they may have stumbled across drug-runners or IRA terrorists, although the use of Peter Dixon's cash card later on the day they disappeared at High Street, Pembroke, and later at Haverfordwest and Carmarthen and again at Haverfordwest, led Police in a different direction.

They were looking for a man who had been seen cycling in the area, but he was never found.