The Crown Office will be asked to decide whether to prosecute in the 30-year-old mystery of an Inverness mother and her baby son.
Renee MacRae's car was found on the A9 in 1976
Renee Macrae and son Andrew disappeared in 1976. Her burning BMW car was found near Inverness.
Northern Constabulary Chief Constable Ian Latimer said an "evidential gap" has been closed.
He said this now justifies going to the Crown and asking it to decide whether to prosecute.
Mr Latimer revealed that progress has been made in the inquiry at a press conference on Friday.
He said a report will go to the procurator fiscal within months.
"We have made progress on the Renee Macrae inquiry," said the chief constable.
"I would say that we have closed the evidential gap as I would describe it.
"There are still some aspects of the inquiry which we want to take further. We are in the process of pulling together in consultation with the procurator fiscal service a detailed report for them to consider."
Mr Latimer added: "It will be very much for the Crown to consider whether closing that evidential gap justifies a prosecution."
The senior officer said that he had to be careful how much he revealed as several aspects of what is a murder inquiry were still live.
Two years ago, police excavated Dalmagarry quarry near Inverness in the hope of discovering whether the 36-year-old's body was dumped there along with her three-year-old son Andrew.
No bodies were found.
Mrs MacRae left Inverness at about 1700 GMT on the evening of Friday, 12 November and her abandoned car was discovered burning at Dalmagarry, at about 2200 GMT.