Double murderer William MacDowell has died in prison today less than a year into his life sentence.
Evil McDowall, 81, murdered his lover Renee MacRae and their young son Andrew in November 1976.
He evaded justice for almost 45 years before finally being found to be responsible for the crime last year. He was sentenced to life in prison for the murders.
Detectives have never found the bodies of the 36-year-old mother or her son, three - and after he was found guilty following a trial at the High Court in Inverness in September, detectives urged the killer to disclose what he did with them so they can be "provided with the dignity they deserve".
But despite the appeal, he never did and the location of their bodies remains a mystery.
On Wednesday, Detective Chief Inspector Brian Geddes - who helped bring MacDowell to justice - urged anyone who could assist to contact police.
"Renee and Andrew's bodies have not been found and recent attempts to encourage William MacDowell to do the right thing, and share any knowledge he may have which could assist the police, were unsuccessful," he said.
"I would urge anyone who may have information about where Renee and Andrew are to come forward so they can be provided with the dignity they deserve."
MacDowell was sentenced just moments after the jury found him guilty of all counts in September.
As judge Lord Armstrong handed MacDowell a minimum of 30 years in prison, sealing his fate to die behind bars, he told the killer:
"These murders appear to have been premediated, planned and carried out in the most calculated way - not a spontaneous event or spur of the moment.
"These appear, in effect, to have been executions.
"You murdered your victims and then disposed of their bodies and personal effects, including the boy's pushchair.
"You then took steps to conceal the crimes you had committed."
As well as being convicted of the murders, MacDowell was also found guilty of attempting to defeat the ends of justice by disposing of their bodies and personal effects.
Authorities had suspected him a number of times as having involvement in the murders, but it was only last year the then frail MacDowell was brought to trial.
The jury of seven men and eight women took just under four hours to come to their conclusion, and as their verdict was read out there were gasps in the court room.
During the trial the court heard MacDowell, who moved to Penrith, Cumbria, killed or abducted Mrs MacRae and their son in a layby on the A9 near Dalmagarry, south of Inverness, on November 12, 1976.
MacDowell and Mrs MacRae - a mother-of-two who was separated from her husband - had been having an affair for more than four years when she vanished, with MacDowell having been questioned numerous times about his connection to the estranged wife of his former boss.
During his first police interview, he refused to admit any association with her, only revealing this in a second interview later the same day.
Even when the case came to trial, MacDowell, who was brought into court each day in a wheelchair by his wife Rosemary, had claimed the crime, if it did happen, was committed by somebody else.
On the night Mrs MacRae and her young son were last seen, the court heard of a "blood-curdling scream" just a few hundred yards from the layby where her BMW would be found burnt out.
The jury were told by Advocate Depute Alex Prentice it was "last utterance of Renee MacRae while alive".
A Police Scotland spokesman said on Wednesday: "Around 11.05am on Wednesday, 15 February, 2023, officers were made aware of the death of an 81-year-old man at Forth Valley Royal Hospital.
"The death is not being treated as suspicious and a report will be submitted to the Procurator Fiscal."
During the trial MacDowell's wife Rosemary told the jury of his ill health.
"He has a very sick liver, very sick kidneys and his heart is trying very hard to keep him alive," she said.
"He's actually a walking dead man, and he has a DNR (do not resuscitate) set up already."
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