DETECTIVES investigating a notorious 40-year-old murder of a mother and son are to dig up part of a major trunk road in the Highlands where it is suspected they are buried.

A section of the A9 between Aviemore and Inverness where ground-penetrating radar (GPR) detected an “anomaly” several years ago will be the focus of a renewed search in the unsolved case of Renee MacRae and her three-year-old son Andrew.

Police Scotland said it would be liaising with the local council and contractors currently upgrading the A9 to establish if the irregularity detected by the radar is the bodies.

The section of the road is due to be dug up next year as part of work to dual the A9, with detectives using the opportunity to investigate the deaths.

Her family will mark the 40th anniversary of her disappearance today saying it was “never too late” to catch the killer.

Mrs MacRae, 36, and Andrew were last seen driving out of Inverness on November 12, 1976.

Later that night, the mother-of-two’s BMW was found burned out in a layby on the A9 near Dalmagarry, 12 miles south of the city. The pair have not been seen since.

She was reportedly on her way to meet her lover, Bill MacDowell, an accountant in her estranged husband’s building company, with the couple said to be planning to start a new life on Shetland.

In 2006, local farmer Brian MacGregor commissioned a GPR scan which identified the “anomaly” beneath the northbound carriageway of the A9 near the village of Moy.

Detective Superintendent Jim Smith from the Police Scotland Major Investigations Team said: “There has been information regarding a ground penetrating radar report carried out on a stretch of the A9 near to the layby where Mrs MacRae’s car was found burnt out.

“Enquiries have established that the area where the report indicated an anomaly in the road surface was not under construction at the time of the disappearance and it was a considerable period of time before that construction work actually commenced.

“We will engage with the contractor which is doing the work on the A9, just to have a look at the area where the GPR report is reporting an anomaly.

“If you were to carry that out on other areas of the A9, it may well have the same anomaly, but we need to explore that further and we will do so in the fullness of time with the contractor.”

The investigation into their disappearance has been subject to ongoing reviews. These include a full cold case review in 2004, which resulted in a month-long excavation of Dalmagarry Quarry and a Police Scotland homicide governance review in 2013.

A statement issued on behalf of the MacRae family said: “Forty years have passed since the disappearance of Renee and Andrew, and as a family we remain collectively heartbroken to have lost a much-loved and cherished mother, sister, brother and friend to many.

“Our message is it is never too late. We are confident these answers will come from the local community and we urge that person to come forward, until such time the person who caused harm to Renee and Andrew will continue to escape justice and we will be without closure.”