The people of Llangolman have long held the belief that a third person was involved in the deaths of brother and sister Griff and Martha Thomas, Ffynnon Samson.

Now, almost three decades following their death, the finger of suspicion is once again pointing towards Pembrokeshire serial killer John Cooper.

Last week, Dyfed-Powys Police confirmed that the investigation into their deaths is going to be re-opened as a result of what they describe as ‘significant developments’ in the way in which forensic evidence can now be analysed.

And while they haven't given any indication as to what they will be investigating, a spokesperson for the force has confirmed that they are not ruling out the possibility that Cooper may have been responsible.

“We are reviewing what limited material we have and we will keep an open mind as we are led by all scientific examinations,” she said.

Griff, 73, and Martha, 70, who was known as Patti, died on December 10, 1976 at their farmhouse in Llangolman. At the time of their death Cooper lived in Jordanston near Neyland but had been carrying out fencing work near the couple's home.

Martha was found bludgeoned to death while Griff was found lying on a wooden settle in the kitchen. He was very badly burned to the extent that only his feet were recognisable.

Following an inquest into their deaths, the coroner recorded verdicts of manslaughter on Martha Thomas and an open verdict on her brother. It was claimed that Griff Thomas had bludgeoned his sister death and then taken his own life.

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As a result, Mr Thomas was denied a headstone at the local chapel, despite being a profoundly religious man and a faithful chapel member all his life.

The coroner's assumption has always been rejected by members of the Thomas’s family as well as locals who knew the couple.

Local campaigner Hefin Wyn has long argued that the case was poorly investigated.

“Everyone who knew the brother and sister sincerely believe that they had not attacked each other,” he said.

“There is now a glimmer of hope that some evidence can be found to prove what people have always believed.

"They had co-habited under the same roof until their seventies, so it is difficult to establish a single motive to support the theory that they attached each other in such a gruesome manner.”

John Cooper’s name has also been linked to the death of Florence Evans, known as Flo, who was found fully clothed in the bath of her home in Rosemarket shortly after the Dixons were shot. Cooper had known Flo for many years as he lived just a short distance away in Jordanston.

Detectives have also investigated Cooper's connectivity with the deaths of Harry and Megan Tooze who were shot at close range at their farmhouse at Llanharry near Bridgend in 1993.