Advances in forensic science caught up with farm labourer John William Cooper more than 20 years after he had shot dead four people, it was claimed this week.

Roger Robson, a fibres expert with LGC Forensics, said tests are available today that had not been in 1985 when brother and sister Richard and Helen Thomas were shot dead at their home, Scoveston Park.

Nor were they available in 1989 when Peter and Gwenda Dixon wereshot as they walked along the Pembrokeshire Coast Path.

But by the time Dyfed-Powys Police launched a "cold case" review of the crimes, LGC Forensics could make a series of discoveries, said Mr Robson.

Mr Robson said that in 1985 and in 1989 forensic scientists had taped numerous surfaces thought to be connected to the crimes, including victims' skin.

The tapings had lifted various items, such as fibres. The tapings had then been sealed.

Many years later, said Mr Robson, he was able to examine fibres using white, blue and ultra violet lights that revealed their chemical and colour make up.

The results, he said, linked both sets of murders to each other, and to a rape and indecent assault that occured in a field close to the Mount Estate, Milford Haven, in 1996.

The examinations also linked the crimes to Cooper, it was alleged.

Mr Robson said: • fibres found on a sock worn by Richard Thomas were also on a pair of green shorts found at Cooper's then home in St Mary's Park, Jordanston. The shorts revealed the DNA of the Dixons' daughter, Julie.

• fibres discovered at a house in Sardis, which Cooper was convicted of burgling, were also on a glove found in a hedgerow near Cooper's home. Two blue fibres from the glove were also found on the shorts.

• fibres from a fleece jacket also found in a hedgerow following the Sardis break in were also found inside a shed at Cooper's house--so many that in Mr Robson's opinion the jacket had been inside the shed.

• two fibres from the Sardis trail glove were found inside the knickers worn by the rape victim.

• 10 fibres from a glove recovered at Cooper's house were found on a shotgun that also displayed Peter Dixon's blood.

Mr Robson said modern forensic testing was so sensitive that he was able to find 28 fibres from the Dixons murder scene which were now of significance. He said they all came from a pair of gloves. Fifteen of the 28 came from a glove found near Cooper's home, and the remaining 13 from a missing glove of the pair.

The various gloves had also been in contact with each other, he added.

Mr Robson said his conclusions included that the glove used in the Sardis break in had also been used in the sex attacks, and that that glove and a glove used in the Dixons murders had both been in contact with the fleece jacket that had once been inside Cooper's shed Mr Robson said he had never worked on a case where there had been so many links between so many exhibits.

Gerard Elias, prosecuting, said it might be suggested that over the years the exhibits had been contaminated because police officers had not been careful enough to keep them apart from each other.

Mr Robson said he had taken part in a two day review of how the exhibits had been handled. The tapings he worked on, he said, had been taken at the time of the crimes and had been sealed.

Cooper, aged 66, now of Spring Gardens, Letterston, denies murdering Peter and Gwenda Dixon, aged 51 and 52, in 1989.

Cooper also denies the murders of brother and sister Richard and Helen Thomas, 58 and 56, who were shot dead at their home, Scoveston Park, four years earlier. The building was then set on fire.

Cooper has also pleaded not guilty to a rape, indecent assault and five attempted robberies.

The trial continues.