It is Britain's longest-running missing persons' case.

On November 12, 1976, Renee MacRae left her home on the outskirts of Inverness with three-year-son Andrew. 

Later that day, officers were alerted to a blazing BMW at a laybay on the A9 near Dalmagarry, which was identified as Macrae. 

READ MORE: It’s incredible Renee McRae’s killer is still out there, says sister 

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.

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.

A timeline of events

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 the night she disappeared - not on her way to visit her sister as previously believed. 

READ MORE: Police to drain Leanach Quarry in search for Renee MacRae 

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 the 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 the report to the Procurator fiscal but Crown Office declare there is insufficient evidence to go to court.

2016: Following a 40th-anniversary appeal, police focus search on the 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.