In December 1976, as news of the tragedy spread around the close-knit community, Dyfed-Powys Police launched a double murder investigation and set up an incident room in the heart of the village.
The case was led by a celebrated detective who had solved the notorious Cannock Chase murders, Det Ch Supt Pat Molloy.
More than 1,200 people were spoken to, with police officers knocking on doors over a five-mile radius.
Over the coming weeks, 572 men provided alibis to police that ruled them out of the investigation.
But as Christmas came and went, and the new year arrived, no leads were emerging.
So the focus of the inquiry shifted.
By late January 1977, Det Ch Supt Molloy reached his conclusion.
He announced that Griff had “probably” killed his sister – possibly by hitting her over the head with a kitchen chair – before starting a fire in which he lay down and died.
For those who had known the siblings throughout their lives, this scenario was incomprehensible.
Mr Absalom, who grew up nearby and was 15 at the time, remembers their deaths sending a “shockwave” through the community.
“I never heard of any falling-out between them, not even a mild argument,” he said.
“These were God-fearing people, chapel was everything to them.”
The siblings were respected and liked in the community and were active members of nearby Rhydwilym Chapel.
Both had lived at Ffynon Samson with their elderly father until his death in 1967.
They continued running the farm into the 1970s before retiring and renting land out.
