Renee MacRae, 36, and her three-year-old son Andrew vanished on 12 November, 1976 – their burnt-out BMW was later found in a lay-by on the A9 south of Inverness.
Now it has been claimed a senior officer involved in an investigation into the notorious case identified a burial site and a suspect who later disappeared.
James Taylor said his friend Sandy Thompson, who passed away some years ago, had been sure MacRae was murdered and buried on the A9 near a flyover. Taylor, 76, reported his concerns to Police Scotland following an appeal for information to mark the 40-year anniversary of the case last year.
“Sandy led a team which spoke to a number of people who knew Renee and which carried out fieldwork as part of the investigation,” he said.
“He spoke to the roads department and came across a foreman who said someone had dug up a section of the road on the day Renee disappeared.
“There was one man he spoke to about the road and showed the evidence they had gathered. Sandy said he knew right away when the man looked at it that the woman was dead, that was where she was buried and this man knew far more about it than he was telling.”
Taylor claims the man fled to the US the day after the interview before returning to the UK later when the case had gone cold.
In 2004, police searched Dalmagarry quarry near the A9 but no bodies were found.
Two years later a report naming a suspect was sent to prosecutors but they decided there was insufficient evidence to take action. Last year police said a ground-penetrating radar report carried out near where MacRae’s car was found had indicated “an anomaly” in the road surface. However, that section of the road had not been under construction at the time of the disappearance.
Detective Superintendent Jim Smith said: “We continue to urge anyone who may have information that could assist the investigation to come forward.”