William MacDowell was sentenced to life in prison with a recommendation that he serve a minimum of 30 years for killing Renee and Andrew MacRae in November 1976.

Police have never found the bodies of the 36-year-old mother or her son, aged three at the time of his disappearance.

Officers now urging the killer to disclose what he did with the bodies so they can be "provided with the dignity they deserve".

Renee MacRae disappeared with son Andrew after leaving their home near Inverness on 12 November 1976. Photo: Police Scotland/PA Wire

Passing sentence after MacDowell was found guilty of murder at the High Court at Inverness, judge Lord Armstrong told him: "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."

He added: "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 of Renee and Andrew MacRae, MacDowell was also found guilty of attempting to defeat the ends of justice by disposing of their bodies and personal effects.

The court heard MacDowell, of Penrith, Cumbria, had killed or abducted Mrs MacRae and her son at a layby on the A9 near Dalmagarry on November 12, 1976.

The double disappearance was one of the longest unsolved murder cases in Scottish criminal history.

On behalf of the family, Morag Govans, Renee's sister and Andrew's aunt, said: “Almost 46 years on, the pain of losing Renee and Andrew in such a cruel and brutal fashion never fades.

“Today there is finally justice for them. It’s a day we feared would never come.

“They were both so precious to us and a day never passes without them both in our thoughts.

“Renee was a compassionate and caring mother. Both Andrew and his elder brother Gordon were her life. She adored them and was so proud of her boys.

“Andrew would be 48 today. He was never given the chance to build his own life.

“The passage of time has not eased the anguish we feel. We have never been able to lay Renee and Andrew to rest or properly mourn their loss.

“Not knowing where their remains lie only compounds the pain.

“Thinking of the terror they both must have felt before they died continues to haunt us.

“We will never comprehend why their lives had to be taken in such a calculated and callous manner by William MacDowell.

“If he has a shred of decency in his body, he will now reveal where they both lie.”

Detective Chief Inspector Brian Geddes said: “Renee and Andrew’s family, and friends, have waited decades for justice and I hope that the outcome in court today can provide some form of closure for them.

“They have carried themselves with absolute dignity throughout and they are very much in my thoughts today.

“The murders of Renee and Andrew MacRae have had a significant impact on people in Inverness, and beyond for decades.

“It is fitting to know that despite the passage of time, justice has finally been served.”

The guilty verdict came after advocate depute Alex Prentice KC told the jury MacDowell was the only man with the motive for killing the pair, as his concern grew that news of his affair would be revealed and what that would mean for his finances and lifestyle.

“Life for Bill MacDowell would change dramatically if it all came out in the open – he would lose his job, his family and his home,” Mr Prentice said.

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 Mrs MacRae’s estranged husband Gordon MacRae and others unknown.

Mr MacRae, who was the director of Inverness firm Hugh MacRae Builders Limited, was asked by the advocate depute if he played any part in the deaths of the pair. The 85-year-old told the jury: “Absolutely none.”

The trial was told that after the couple split, they had an “amicable” relationship, with Mr MacRae aware his estranged wife was involved with someone else and that Andrew was not his child.

He had provided her with a home in Cradlehall Park, Inverness, and with a metallic blue BMW.

The car was found burnt-out at the Dalmagarry layby, south of Inverness on the A9, on the night Mrs MacRae and her son were murdered.

Catherine Johnstone told the court her mother Eva McQueen had heard a “blood-curdling scream” just a few hundred yards from the layby at Dalmagarry Farmhouse.

Mr Prentice told the jury this was the “last utterance of Renee MacRae while alive”.

MacDowell’s company Volvo was spotted nearby, the court heard, the very car he admitted burning part of the boot of.

Ms Govans, now 84, told the trial of her sister’s devotion to her two boys, and said her concerns had grown for her welfare when detectives visited her home after the disappearance.

Ms Govans said: “I was very worried. I knew something dreadful had happened to Renee and Andrew. I knew Renee would never have gone away and left her other son Gordon behind.

“I know Renee wouldn’t have put me through that. She would have contacted me if she had gone anywhere.”

Renee MacRae case: William MacDowell guilty of murdering woman and three year old son in 1976