Two carers have been convicted of murdering a 19-year-old woman whose death they covered up for 20 years and whose body has never been found.
Edward Cairney, 77, and Avril Jones, 59, killed Margaret Fleming in December 1999 or January of the following year.
The authorities only became suspicious in October 2016 when concerns were raised about a benefits claim made by Jones on Ms Fleming's behalf.
A huge police search operation has failed to find any trace of Ms Fleming.
Cairney insisted during the trial at the High Court in Glasgow that Ms Fleming is still alive and had gone to London.
He claimed that she regularly returned to their home in Inverkip, Inverclyde, when she needed money.
He also claimed Ms Fleming, who had learning difficulties and went to live with the couple after her father's death in 1995, fled out of the back door when police first arrived at the house, which is known as Seacroft, to search for her.
But a jury found Cairney and Jones guilty of murder after a seven-week trial.
Jones was also found guilty of fraudulently claiming £182,000 in benefits by pretending that Ms Fleming was alive.
Lord Matthews, the trial judge, said he would pass sentence next month after social work and medical reports are compiled on the pair.
Speaking outside court, Det Supt Paul Livingstone - who led the investigation - said Ms Fleming had been a "very vulnerable young woman who was manipulated, abused, neglected and ultimately murdered by the two people who should have been looking after her".
He said it was clear that Cairney and Jones had been motivated by money and kept the teenager in conditions that were "utterly disgusting and uninhabitable" before killing her.
He added: "We will never know just how Margaret was killed. What we do know is that she lived her last days in what can only be described as a living hell.
"She must have felt that she was alone in the world with no-one coming to help her, which is just heartbreaking to think of."
Inverclyde Council said it was asked by the procurator fiscal not to carry out an investigation before the trial concluded.
A spokesman said: "Inverclyde's multi-agency public protection committees will now work with all the organisations involved in Margaret's case on a full, detailed examination of the events leading up to her tragic death."
The last independent sighting of Ms Fleming, who briefly attended James Watt College before effectively being held prisoner by the couple, was when Jones' brother Richard saw her on 17 December 1999.
She did not join the rest of the family for Christmas dinner the following week. On 5 January of the following year, Jones told her mother that Margaret had run off with travellers.
There have been no sightings of her since, and detectives were unable to establish how she died or what happened to her body - although a former firefighter told the trial he once smelled what he believed was burning human flesh coming from a bonfire at Cairney and Jones' home.
The pair tried to cover their tracks by travelling to London, and letters purporting to be from Ms Fleming were posted to their home in a bid to cover up their crime.
Bogus diary and calendar entries were also written to suggest Ms Fleming had left the house voluntarily.
Despite this her benefits continued to be paid into Jones' account, without challenge, for more than a decade.
The trial heard that a benefits investigator attempted to visit Ms Fleming in June 2012 but was told by Jones that she would not see her.
The investigator said a duty social worker should have visited the "totally chaotic" property to follow up on the young woman's welfare, but no-one did.
When police were finally alerted four years later it was as a result of an application for Personal Independence Payments (PIP) - which had been filled out by Jones.
In it she wrote that Ms Fleming "needs constant care", had self-harmed and was "caught eating out of a dog bowl".
A social worker phoned Jones to offer help and was told Ms Fleming had not been to the doctor, despite picking a hole in her head.
Police Scotland subsequently launched a missing persons' investigation in October 2016 but an extensive search of the house - which included two downstairs bedrooms full of rubbish - and its grounds failed to uncover any trace of Ms Fleming.
Despite their suspicions, detectives did not have enough evidence to charge the couple - but that changed after Cairney made a series of outlandish claims in interviews with journalists including BBC Scotland's Suzanne Allan in October 2017.
He said Ms Fleming had become a "gangmaster" and was also "buying and selling" drugs.
Cairney later told the trial that he had met Margaret in London two years ago.
Cairney and Jones were detained on 25 October of that year at Glasgow Central Station as they attempted to board a train to London while carrying £3,500 in cash.