THE sister of a housewife whose disappearance 40 years ago along with her three-year-old son remains Britain’s longest running missing persons case has insisted someone is shielding a “monster” behind what she believes is a double murder.

Morag Govans, 76, who rarely speaks about the case – which is thought to be among the most baffling in the history of Scottish policing – said she finds it “incredible” that the culprit behind the double disappearance has not yet been traced.

Speaking on the approach to case’s 40th anniversary, Ms Govans urged the Crown to sieve through the evidence in a renewed bid for justice. Renee MacRae and her three-year-old son, Andrew, were last seen on the afternoon of November 12, 1976, driving south out of Inverness.

Later that evening, their car was found burnt out in a lay-by on the A9.

Almost every officer in the Highlands took part in a search which continued off and on for a year, but the pair have never been found.

Northern Constabulary re-examined the case in 2004 and named a suspect in a report to the procurator fiscal in October 2006. However, the Crown Office declared there was insufficient evidence to go to court.

It was believed Ms MacRae, and her son, were due to meet her secret lover, her husband’s company accountant Bill MacDowell, that Friday evening to spend a weekend away.

Mr MacDowell later revealed that the child was his son – a fact he only confirmed a few days after their disappearance sparked a major investigation by Northern Constabulary.

Ms Govans said a slew of evidence has been presented to the Crown Office and that former Chief Constable Ian Latimer thought there had been sufficient evidence to prosecute a suspect when the last report was submitted in 2004.

“That was after he ordered the search of the quarry near the Dalmagarry lay-by when a former policeman thought he had detected the smell of decomposing flesh all those years ago,” she said.

“Sadly, nothing was found. But I still find it incredible that no-one has ever been taken to court.

“I am disappointed they haven’t.”

And she added: “I know there is someone out there who could come forward and give us the information that we need to find Renee and Andrew. I don’t understand how anyone can shield a monster like that.

Ms Govans believes the bodies of her sibling and nephew lie within five or 10 miles of the lay-by where the car was found torched. Dalmagarry Quarry, next to the A9, was twice searched by police investigating the mysterious disappearance but Ms Govans believes it was not checked properly at the time.

And she said: “It has got to be somewhere. Two bodies, a pushchair, and whatever luggage they had – it’s a lot of things to dispose of.

“I would like to see the Crown Office have a go in court.

“So many years have gone by, I wonder if they will ever solve it. But bringing someone to court could make the difference.”