On this day in 1976, Renee MacRae left her home on the outskirts of Inverness with three-year-son Andrew. 

Later that same day, police were alerted to a blazing BMW on the side of a road. 

The car, which would soon be identifed as Renee's, was found torched in a laybay on the A9 near Dalmagarry.

Police launched a double murder hunt but the bodies of Renee, then 36, and toddler Andrew have never been found.

At the height of the investigation, hundreds of police, military personnel, and volunteers took part.

Canberra bombers with heat-seeking devices flew over the Highlands hoping to pick up a reading which could indicate a body.

Divers and specialist underwater camera equipment were used to search lochans and flooded quarries.

More than four decades later, police have renewed the 42-year investigation in a bid to give the family of Renee and Andrew closure. 

Read more: Police to search under road in Renee and Andrew MacRae murder inquiry

HeraldScotland:

Detectives with Renee's burned out BMW (Photo: Police)

'I will never give up hope of getting justice'

Speaking on the 42nd anniversary of her sister's disappearance, Morag Govans said she will never give up hope of getting justice for her family.

She said: "More than four decades on the pain of losing Renee and Andrew doesn't ease. Not a day goes past that both are not in my thoughts.

"Andrew was just three-years-old, a mischievous and fun loving wee boy. It is impossible to take in that his life was brought so cruelly to and end at such a young age.

"He would have turned 45 in October and I often wonder what he would have been doing now with the life that he was never given the chance to build.

"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.

"Gordon was only eight and has lost the love and guidance of his mum and brother."

HeraldScotland:

Read more: It’s incredible Renee McRae’s killer is still out there, says sister

She added: "Even after the passage of time I believe that there are people who know what happened to Renee and Andrew and I will never give up hope of getting justice for them both.

"I appeal for anyone with any information to come forward and for others to examine their conscience to end 42 years of pain and anguish to allow us to grieve for Renee and Andrew."

Ms Govans previously told the Herald how it was "incredible" that a culprit had not been caught, and how she believed someone was "shielding a monster".

Timeline of Britain's longest running missing persons case

1976: Renee MacRae and toddler Andrew leave their home on the outskirts of Inverness - later that night, Renee's burnout BMW is discovered a few miles south of the city.

1976: Investigating officers discover Renee had been having affair for four years, and was on way to visit lover on night she disappeared - not on her way to visit her sister as previously believed. 

1979: With leads exhausted, the case winds down.

2004: Grampian Television Unsolved documentary renews interest in the case, prompting police to reopen the investigation.

2004: A cold case review leads to excavation of Dalmagarry quarry. Twenty-thousand tonnes of earth and 2000 trees are removed but nothing is found.

2006: Northern Constabulary name a suspect in report to the Procurator fiscal but Crown Office declare there is insufficient evidence to go to court.

2016: Following 40th anniversary appeal, police focus search on section of A9 between Aviemore and Inverness where they believe the pair may have been buried.

2018: On October 2, 2018, it was reported that Leanach quarry was being searched in relation to the case.

'Forty-two years is no barrier to justice'

The murder investigation into Renee and Andrew's disappearance has spanned decades, with police carrying out two large excavations near where the charred car was found.

The detective heading up the case today is hopeful than foresnic advancements will finalyl give the family answers.

He also called on an anonymous source who wrote to Northern Constabulary in 1982 about activity at an unnamed quarry.

Detective Inspector Brian Geddes said: "All the indications are that Renee and Andrew came to harm 42 years ago and as such this is being progressed as a murder investigation.

"The initial investigation and the various reviews and re-investigations since 1976 appear to have been very thorough and have generated a great deal of material. 

"We are applying the most modern investigative techniques in a bid to progress the investigation and this will include utilising advances in forensic science.

"Our goals are to bring a person, or persons, to justice and to locate the remains of Renee and Andrew in order to bring some form of closure to Morag and the rest of the family."

HeraldScotland:

He added: "The chances are that person or persons responsible for the murders of Renee and Andrew will have enjoyed a life, something which was denied to Renee and Andrew ...

"Specifically, I want to take this opportunity to appeal to someone who wrote anonymously to Northern Constabulary in 1982 regarding information surrounding activity at an unnamed quarry on November 12, 1976. 

"It appears that this person had moved away from the area in the subsequent years. If you recognise yourself as the writer of this letter then I urge you to get in touch with the investigation team.

"Forty-two years is undeniably a long time, however, it is certainly no barrier to justice.

"Someone out there knows what happens to Renee and Andrew and I hope this appeal today serves as a reminder that it is never too late to come forward with information."