This week marks the 10th anniversary of York woman Claudia Lawrence's disappearance.
The 35-year-old chef vanished after failing to turn up for an early-morning shift at a University of York canteen on March 19, 2009.
Interview: Claudia Lawrence's father Peter admits he may never see her again
Police claim that a lack of co-operation from her associates has hindered the investigation and means her disappearance, which is being treated as a suspected murder, remains unsolved a decade on.
The dreadful lies told over Claudia Lawrence's disappearance
Claudia was last seen near her home in the Heworth area of York on the afternoon of March 18, and called her mother that night, as well as sending a friend a text message. She has not been seen or heard from since. Nine people have been arrested and questioned, but nobody has ever been charged.
These are the main theories about what might have happened to her.
Police believe that Claudia left home for work, or at least had been preparing to, on the morning of March 19 - there were breakfast dishes in the sink and she'd made her bed. A rucksack containing her chef's uniform has never been found. Her mobile phone was turned off around midday and did not leave the area before it vanished from the network. Claudia's car was in the garage for repairs, so she had been walking to and from work that week. The initial theory was then somebody in a car had picked her up along the route.
In the early days after her disappearance, the possibility that Claudia had chosen to disappear of her own accord was explored. She was known to visit Cyprus and had made friends on the island whom she stayed in contact with when back in the UK. The last text message she received before she went missing was from a bar worker she had met there, and it was thought she may have been considering job opportunities abroad. Detectives visited Cyprus as part of the investigation six months after she went missing, but did not find any leads. Her passport and bank cards were found in her house, meaning it would have been difficult for her to leave the country voluntarily.
A complex personal life
Police are convinced that the person or persons who harmed Claudia are local to York. Her local pub, the Nag's Head, played an important role in her social life and detectives focused their investigations on its clientele. Several mysterious leads were discovered - a DNA sample taken from a cigarette butt in her car was never identified and police traced her movements to the York suburb of Acomb a few weeks before she disappeared, but were never able to establish why she was there. Police have expressed their frustration at the belief that people with vital information have refused to come forward to protect their own reputations and private lives. Claudia's father, Peter, has acknowledged the likelihood of this - but has appealed to these witnesses to think of the pain Claudia's disappearance has caused his family.
Police reiterated recently that they do not believe a stranger was involved - and that more than one person knows what happened to Claudia. They believe the truth may be revealed in future if there is a disagreement between the perpetrators and one decides to come forward.
An overnight visitor
An alternative theory is that Claudia was harmed on the night of March 18, after the last sighting of her, by someone who visited her house that evening. A person dressed in dark clothes and carrying a rucksack was picked up on CCTV near the alleyway behind her home at around 7pm that night. They were never identified.