Detailed searches are now underway of Leanach Quarry as part of the investigation into the murders Renee and Andrew MacRae.
This comes after the removal of water from the site near Inverness.
Renee MacRae and three-year-old Andrew were last seen driving out of Inverness on November 12, 1976.
The 36-year-old mother-of-two’s BMW was found burned out in a lay-by on the A9 near Dalmagarry, 12 miles south of the city, but the pair were not seen again.
Officers have now begun searching the quarry, which has been drained of water, in the latest development of what police are treating as a murder investigation.
The site was previously deemed too dangerous to use divers but police are “extremely confident that vital evidence” will be found after what has been described as “fantastic progress”.
DI Brian Geddes said: “The team involved at Leanach Quarry have put in an incredible amount of work and their tireless efforts mean we have now started the detailed searching phase of the operation.
“Pumping the water clear was a huge challenge, but we have made fantastic progress in a very short time.
“Silt and debris from the bottom of the quarry are now being removed by lorry to undergo forensic tests at another location.
“The whole team remains extremely confident that vital evidence we believe was hidden in Leanach will be recovered in the coming weeks.
“I want to reassure the family and friends of Renee and Andrew that we will not be leaving here until every last inch is searched.”
Anyone who believes they can assist police is asked to contact 101 or you can e-mail a dedicated inbox at SCDHOLMESInverness@scotland.pnn.police.uk. You can also contact Crimestoppers anonymously on 0800 555 111.