MURDER cops probing Renee MacRae and her toddler’s mystery disappearance 43 years ago are to drain a flooded quarry.
Detectives believe the pair’s remains could be buried within 100ft Leanach pit near Inverness.
Renee, 36, and Andrew, three, vanished from the city in 1976.
A source said of the huge operation: “Key evidence may be hidden there — and potentially bodies.”
And it’s hoped fresh clues about the unsolved murders have given cops their “best chance yet” of finding out what happened.
Detectives probing the mystery will return to Leanach Quarry near Inverness — where previous trawls came to nothing — after public appeals sparked new leads.
Experts are poised to begin draining the “dangerous” 100ft pit within days, before search teams move in to hunt for the remains of Renee and Andrew among the layers of mud and silt.
A source close to the investigation said: “They believe this is the best chance they’ve had of solving this case.
“It was triggered by new information that came in following recent appeals. It’s very significant and it’s led them back to the quarry, which has always been an area of interest.
“It’s a massive undertaking to search the entire quarry, but the cops obviously believe they have good reason to do so.
“It’s too dangerous just to be searched, so in the next few days they are going to pump water completely out the quarry.
“It’s a major operation that will see vast amounts drained over a period of weeks.
“As far as we know, it’s a first and there’s never been an operation like it across the UK.
“The main focus of the team will be to get to this evidence and to recover the bodies if they are there.”
Renee and Andrew vanished on November 12, 1976, after dropping older son Gordon, nine, at the home of her estranged hubby, also Gordon.
She was then supposed to be driving to meet her lover Bill MacDowell, her ex’s accountant — who was Andrew’s biological dad.
But her burnt out BMW was found 12 miles from her Inverness home in a layby on the A9. A bloodstained rug was in the boot.
Renee’s sister Morag Govans has told of her agony that no one has faced justice for her loved ones’ murders, despite a cold case review concluding there was insufficient evidence for a trial.
In 2016, cops sent prosecutors a report naming a suspect who may have killed the pair. But it was ruled there wasn’t enough proof to bring charges.
The treacherous quarry — a fly-tipping spot — was first searched in 1978, when divers using underwater cameras reportedly caught sight of a head inside a plastic bag.
Navy underwater crews were immediately drafted in to help scour the murky waters. But the sacks of rubbish they retrieved failed to shed any light on Renee and Andrew’s whereabouts.
A second unsuccessful trawl was carried out last year at the site, which lies close to the battlefield at Culloden Moor.
Police also searched Dalmagarry Quarry, 12 miles south of Inverness, at the time of Renee’s disappearance.
They returned in 2004, drafting in forensic archaeologists and anthropologists to sift 35,000 tonnes of soil from the disused trench.
But the latest operation, which has involved months of careful planning, is seen as a “major development” for the team.
It’s understood they began scoping the area and studying the layout of the quarry around October 2018, just as a plea for information was made to mark what would have been Andrew’s 45th birthday.
At the time, detectives released a new picture of the missing lad, along with a photo of a Silver Cross pram owned by his mum.
Police later hailed the public response to their appeal, revealing they’d received more than 20 calls.
Detective Inspector Brian Geddes also begged the author of an anonymous letter found in police files from 1982 to come forward.
The informant had claimed to be “in a quarry the night Renee disappeared and heard something potentially suspicious”.
Our source said: “The team have been reviewing this case and it’s led to the major investigations team returning to the quarry with renewed determination.”
It’s understood the huge pit will be sealed off as early as today as preparations get under way to start draining it later this week.
Once emptied, forensic experts will move in to conduct a fingertip search of its muddy depths.
The insider said: “It will be a detailed search that will see investigators going through tonnes of material with a fine tooth comb, looking at everything there. A number of different organisations are involved, including search teams and officers guarding the site.”
In November last year, we told how Morag, now in her eighties, of Beauly, Inverness-shire, dreamed of the day she could finally lay Renee and Andrew to rest.
She said: “To have a funeral would mean everything to me. I’m worried I could pass away before anything is found.
“Even after all this time I believe there are people who know what happened.”
Cops last night confirmed a new hunt is set to begin for the missing mum and son — but refused to give any more details.