'Evil' labourer convicted of two 1980s double murders after cold case review

A farm labourer has been jailed for life over the murders of four people in Pembrokeshire after evading detection for more than 20 years.

John Cooper, 66, from Letterston, Pembrokeshire, used a shotgun he carried with him during a campaign of robberies and burglaries to kill siblings Richard and Helen Thomas at their Pembrokeshire farm in 1985 and Peter and Gwenda Dixon, who were on the last day of their holiday in west Wales when they were murdered on a cliff path in 1989.

The convictions yesterday after an eight-week trial at Swansea Crown Court resolve two crimes which had perplexed police for decades and were only solved after a cold case review secured forensic evidence using techniques unavailable at the time of the killings.

Cooper, described by detectives as "very dangerous and evil", was told that he will remain behind bars for the rest of his life. He was also found guilty of raping a 16-year-old schoolgirl at knifepoint and sexually assaulting another during an armed robbery in Milford Haven in 1996. The court heard that the farm worker meticulously planned his crimes using his knowledge of the area surrounding his Pembrokeshire home to cross farmland unnoticed.

He killed Helen Thomas, 54, and her 58-year-old brother at their remote mansion near Milford Haven three days before Christmas during a break-in. Police believe he was disturbed by Mr Thomas, turning his shotgun on the brother and sister before pouring diesel around the three-storey farmhouse and setting it ablaze.

The Dixons encountered Cooper during a final walk along the Pembrokeshire Coastal Path at Little Haven. The gunman took the couple to an improvised hideaway, tied 51-year-old Mr Dixon's hands and demanded the PIN code to his bank cards before shooting them at point-blank range.

After the killings, Cooper took out money using the stolen bank card and sold Mrs Dixon's wedding ring for £25.

Judge John Griffith Williams told Cooper: "I am confident that you will never express any remorse and so help the victims come to terms with their loss... the murders were of such evil wickedness that the mandatory sentence of life will mean just that."

The killer, who repeatedly interrupted the judge during sentencing to claim evidence had been kept from the jury, frittered away £90,000 won in a spot-the-ball competition in 1978. The prize, equivalent to £1m today, should have made Cooper financially secure for life but instead he lost the cash on disastrous property deals.

The breakthrough for Dyfed-Powys Police came after a review in 2006 of material gathered during an investigation which in 1998 had led to Cooper being jailed for 16 years for a string of burglaries. Tests uncovered vital forensic evidence – a blood speck on his shotgun and DNA on a pair of shorts – linking him to the murders of the Dixons. He was arrested in 2009.