Detailed searches to begin at Inverness quarry site in Renee MacRae investigation
It comes after the removal of water from the site near Inverness, which got underway last month.
Renee MacRae (36) and her three-year-old son Andrew disappeared on November 12, 1976 and their burnt-out BMW car was found in a layby at Dalmagarry, 10 miles outside Inverness.
They had been due to spend the weekend with Mrs MacRae's secret lover Bill MacDowell who later admitted he was the father of the little boy and had been employed as an accountant with Mrs MacRae's estranged husband Gordon's building firm.
The bodies of mother and son have never been found.
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.