Police searching for a woman who has not been seen in public for 17 years say they cannot rule out the possibility that she has come to harm.
Margaret Fleming was only reported missing from her home in Inverkip in Inverclyde six months ago.
But it emerged that no-one except her carers had seen her since 1999.
Officers, who searched the house for months, said she "could have had an accident, possibly wanted to be missing or even something more sinister".
Margaret, who will now be 36, was reported missing by her two carers on 28 October.
However, apart from the carers, the last independent sighting of her was at a family gathering on 17 December 1999, when she was 19.
Police were initially asked to call at the remote house, next to the coast on the road between Inverkip and Wemyss Bay, by social work officers.
Det Ch Insp Paul Livingstone told BBC Scotland: "Police were carrying out routine inquiries on behalf of a partner agency and that's when Margaret was reported missing."
"Given the timescales involved it was passed to ourselves here at Major Investigations Teams."
In the years since Margaret was last seen, there has been no trace of any contact with the outside world.
Margaret, who was said to have learning difficulties, had never had a job and had no presence in the online world.
Det Ch Insp Livingstone said Margaret's bank account had not been accessed for many years but confirmed she was in receipt of benefits.
He said: "The carers managed that for her. They ensured the money that was for Margaret was used for her."
The detective said the property where they lived was a five bedroom house called Seacroft in a relatively remote area of Inverclyde.
Police began a search of the house in November and extended into the garden, where excavation work was carried out on half an acre of land.
Forensic experts said they were sifting through the house and garden to find any documentation, clothing and personal items that could assist in finding her.
Det Ch Insp Paul Livingstone said: "There have been extensive inquiries over the past six months as we try to piece together Margaret's life.
"A team of dedicated officers have been sifting through thousands of items, paperwork, documents, and articles taken from the house.
"We've been in contact with around 1,200 individuals and organisations who may have had contact with Margaret in an effort to trace her and over 200 have still to get back to us so we have some lines of enquiry still to follow up."
The detective said officers had taken 500 witness statements and extended the search to 500 metres beyond the house into nearby water and woodland.
He said the search had now finished.
Det Ch Insp said: "Whilst we are keeping an open mind - her carers state that Margaret has a private side to her life, possibly having friends that they are not aware of - we cannot rule out the possibility that she has come to harm in some way.
"By this I mean that she could have had an accident, possibly wanted to be missing or even something more sinister."
He added: "We remain in contact with Margaret's mother, who understandably is shocked and distressed at her disappearance.
"Her carers have been assisting us with our enquiries, and the strength of feeling and support from local residents in the Inverkip area has been welcomed."
He said Margaret was still being considered a missing person and appealed for anyone who may have seen her since 1999 to get in touch.
28 October 2016 - Margaret Fleming reported missing by her carers. The 36-year-old woman was described as 5ft 5in, with collar length black hair and brown eyes. She is described as being of heavy build.
10 November - Police reveal that Margaret has not been seen in public for 'quite some time'. They appealed for people who knew her when she was at James Watt College in Greenock 20 years ago.
Police launch a large-scale search with police divers deployed and officers are spotted combing a large area of ground near the electricity sub-station in the hillside above the A78.
Police say they have limited information and are unable to issue a recent photograph.
Local residents say they have never seen Margaret.
26 November - Despite numerous appeals and searches by specialist police teams, including the mounted unit, divers and dog branch, there has been no trace of Margaret. Chief Inspector Elliot Brown said: "This has been one of the most challenging missing person inquiries of my career because of Margaret's secluded lifestyle."
30 November - Police search the home of the carers
12 December - Search moves from the house to the garden. Police say that, apart from her carers, the last independent sighting of Margaret was on 17 December 1999, at a family gathering. Officers say they have no trace of her having a job, no friends have come forward and she had had no contact with any agencies. Detective Chief Inspector Paul Livingstone said: "Margaret's carers have said that they believe she has a private side to her life and that she may have friends that they are not aware of."
13 December - Police start to dig up garden.
16 December - Drone footage shows garden being dug up
21 December - Drones banned from flying over the site
28 April 2017 - Police say search of house, garden and surrounding area is complete but investigations are ongoing