Ten years ago, three-year-old Madeleine McCann vanished from a holiday apartment in Praia da Luz, Portugal sparking one of the largest missing persons hunts in history.
The case sparked an unprecedented level of media interest but a decade later there have still been no definitive breakthroughs and her fate remains unknown.
Although rumours, conspiracies and speculation still run rife, there are a handful of more likely theories behind her disappearance.
Burglary gone wrong
When Scotland Yard launched its review of the investigation in 2011, officers identified a string of break-ins at apartments across the Algarve, including in Praia da Luz.
They found that there had been a four fold increase in the number of burglaries in that area in the months running up to Madeleine's disappearance.
The patio doors of the McCanns' apartment had been left unlocked on the night of May 3, meaning opportunistic thieves could have had easy access.
The burglaries were thought to have been the work of a gang of roving thieves and police began exploring the theory that Madeleine may have been snatched after waking up and disturbing intruders.
Detectives identified a list of mobile phones that had been in the resort at the time of Madeleine's disappearance in an effort to trace possible suspects.
Bogus charity collectors
In 2013 Scotland Yard announced that investigators were looking into the activities of a group of bogus charity collectors who had been spotted knocking on doors in Praia da Luz around the time Madeleine went missing.
Witnesses were able to provide two e-fit images of men who were seen visiting apartments in the resort on the pretence of collecting money for orphans.
It was thought the criminals had been posing as charity collectors, but were also using the ruse to scope out apartments to burgle. Police issued a series of photo-fit images of suspects they said may have been hanging around the Algarve during that period and the pictures featured on a BBC Crimewatch appeal.
Stolen to order for childless couple
With no evidence to suggest Madeleine is dead, it has long been suggested that she may have been stolen to order by criminals acting on behalf of a wealthy childless couple.
Witnesses claimed to have seen suspicious characters around the resort in the days before her disappearance, who could have been acting as spotters, searching for a child that fitted the requirements.
There were a number of sightings of suspicious blonde haired men who were seen hanging around the Ocean Club resort in the days leading up to Madeleine's disappearance.
Witnesses also claimed to have seen two blonde men on the balcony of a nearby apartment, just two doors from where the McCanns were staying. They were said to have been speaking Dutch or German, leading to appeals being broadcast in both of those countries.
The head of the investigation at the time DCI Andy Redwood, said: “Madeleine McCann’s disappearance does, on one reading of the evidence, have the hallmarks of a pre-planned abduction. That would undoubtedly have involved reconnaissance and so we are really keen to understand who these people are.”
Abducted by a paedophile gang
Police have also been forced to explore the possibility that Madeleine was abducted by a sex attacker who had been operating throughout the Algarve for several years.
Police identified nine sexual assaults and three "near misses" on British girls aged between six to 12 in the three years before Madeleine went missing. In one case from 2005, a ten-year-old girl was assaulted in an apartment Praia da Luz, close to the spot from where Madeleine vanished.
An Irish family who had been on holiday in the resort in May 2007, reported seeing a man carrying a child around Madeleine's age towards the beach at around 10pm on the night she disappeared. Martin Smith from Drogheda, Co Louth in the Republic of Ireland, gave the description to Portuguese police at the time but little was done with the information.
In 2008 he met with private detectives working for the McCann family and produced an e-fit image of the man he had seen. But the image was not placed in the public domain at the time because it was thought Madeleine had been abducted almost an hour earlier.
In 2013 police admitted that the original timeline was probably wrong and the image featured in a Crimewatch appeal.
Another theory that has emerged is that Madeleine was not abducted from the apartment, but was actually snatched or came to harm after wandering off.
The three-year-old was asleep in the ground floor holiday flat, with her one-year-old twin brother and sister Sean and Amelie.
Her parents Kate and Gerry were having dinner with a group of friends at the complex's Tapas restaurant around 50 yards away. While the front door remained locked, the patio doors were left open so the parents could slip in an out easily to check on the children's welfare.
It has since been suggested that Madeleine may have woken during the evening and got up to go and look for her parents. Had she negotiated her way out of the apartment - which was the last one on the block - she could have wandered into the main road and been hit by a driver who then panicked.
Alternatively she could have then been snatched by an abductor. But for the theory to be plausible, Madeleine would have had to close the heavy sliding patio doors behind her, something which seems unlikely.
Taken to North Africa by people traffickers
There have been almost 9,000 supposed sightings of Madeleine McCann around the world since her disappearance 10-years ago.
One theory that emerged was that the three-year-old was targeted by people smugglers who whisked her away to nearby Spain and then across the Strait of Gibraltar into North Africa.
Gangs known to be operating in the region could have concealed her easily and then moved on to avoid detection. Investigators working on the case have explored numerous leads in Morocco, including several sightings which initially looked very promising.
In 2007 just months after Madeleine disappeared, a tourist took a photograph of a group of women in Tangiers wearing traditional North African dress and carrying a blonde girl who bore a striking similarity to the missing youngster.
However, the group was subsequently tracked down and the girl was identified as the five year old daughter of a local farmer. Morocco and neighbouring North African countries have remained key areas in the ongoing investigation.