Despite attracting huge publicity, and being featured on shows such as BBC’s Crimewatch, both double-murders – millionaire farmer Richard Thomas, 58, and his sister Helen, 54, in their Scoveston Park home near Milford Haven, and four years later marketing manager Peter Dixon and his wife Gwenda, whose blasted bodies were discovered in a cliff-edge hideaway on one of Pembrokeshire’s lonely rural paths – remained unsolved for years. Then, in 2006, Dyfed-Powys Police re-examined the evidence using modern techniques, in a final attempt to solve the crime.

They had plenty of time to build their case, because John Cooper, the man they suspected, and finally identified as the killer, was at that time doing 16 years in prison for multiple burglaries. Within months of his release, he was re-arrested and charged with what were to be described as two of the most infamous double-murders ever in the history of South Wales…