01:51, UK,
Wednesday 03 May 2017
By Martin Brunt, Crime Correspondent
There have been hundreds of different theories about how Madeleine McCann went missing, but they mostly fall into six main categories.
:: The parents
The first senior detective on the case, Goncalo Amaral, believed Madeleine died in the family's rented holiday apartment and her parents covered up her death and disposed of her body.
The suspicion appeared to be supported when British sniffer dogs - trained to detect body scent and blood - reacted in the apartment and in a car which was hired by Gerry and Kate McCann about three weeks after Madeleine disappeared.
The misinterpretation by Portuguese investigators of the results of forensic swabs taken from the apartment and car led to Kate and Gerry McCann being questioned and made "arguido" - official suspects.
The couple were ruled out when the Portuguese case was closed, unsolved, after 15 months. They have always denied any part in their daughter's disappearance and two Portuguese investigations and a Scotland Yard inquiry have found no evidence to suggest otherwise.
Would two doctors, trained to preserve life, choose not to raise the alarm, but instead dispose of their daughter's body, and have the means to do so without a car and in a foreign country, before joining friends for dinner as though nothing had happened? And keep such a secret for years while drawing global attention to themselves and their campaign to find Madeleine?
:: Burglary-gone-wrong
Madeleine wakes up and disturbs a burglar.
He panics and attacks her, then decides to carry her off, dead or alive.
In 2014, Scotland Yard - through the Portuguese police - questioned four local suspects on this theory. They came under suspicion because of their mobile phone contact and location at the time of Madeleine's disappearance, as well as their backgrounds, but were later ruled out. The Yard is still pursuing the general theory, but Portuguese police dismissed it.
Wouldn't a burglar who is disturbed simply get out of the apartment? Detectives say you cannot apply cold logic to a criminal reacting under pressure. If you have eliminated other theories, you pursue the one where you have some evidence, however thin it is, until you disprove it as well.
Such a spontaneous act is likely to lead to mistakes, a trail of evidence and detection.
:: Attacked by a local paedophile
Madeleine was the victim of a paedophile who snatched her and later killed her - burying or hiding her body, possibly in the sea.
Witnesses saw several suspicious men watching the McCanns' apartment in the days before and on the day, though Scotland Yard said some have been eliminated.
This was the theory pursued by Portuguese detectives who reopened their investigation in 2011 after studying a series of attacks in resorts along the Algarve coast in the years up to 2007. A man had entered the apartments and villas of mainly British holidaymakers and molested young girls while they slept.
There were attacks in Albufeira, Carvoeiro and Silves.
Portuguese investigators believed one man was responsible for those attacks and identified former Ocean Club waiter Euclides Monteiro as their suspect. He was already dead after being killed in a freak tractor accident in 2009.
He was eventually ruled out by DNA evidence, but that means a predator or predators were still at large when Madeleine vanished.
Detectives argue that paedophiles prefer older, pre-pubescent victims and only rarely would risk taking a child from inside a building. They tend to panic after the deed and the bodies of their victims are eventually found not far away.
Such a serious attack is often the culmination of a history of escalating behaviour by a sex predator who may already have a criminal record for lesser offences and be more easily identified.
:: Abducted by childless couple
Madeleine was taken by or for a couple who could not have children of their own or had lost a child. This could also apply to a woman - or even a man - who wanted a child to keep.
The hole in this theory is that such a kidnapper would be more likely to take one of the younger children, Madeleine's twin siblings Sean and Amelie, who were sleeping beside her and were only two years old.
They would have been less likely to wake up and resist and would remember far less or nothing at all of their old life as they grew up.
The theory would be most welcomed by Madeleine's parents because it would probably mean that she is alive and being cared for.
:: Taken by child traffickers
Madeleine was kidnapped by a gang, taken abroad and sold into slavery. In 90 minutes she could have been driven to the Spanish border or put on a boat in nearby Lagos marina and taken to Morocco hours before police suspected Madeleine had been abducted.
It was an early theory explored by Portuguese investigators after a report that Madeleine had been photographed on the beach by a stranger. It could have been part of a selection process.
Human trafficking gangs are known to operate in the northwest African country of Mauritania, which in 1981 became the last country in the world to abolish slavery. Many are still thought to be kept in slavery there today.
Several witnesses reported possible sightings of Madeleine in Morocco, a country on the trafficking route to Mauritania. Her parents went to Morocco to make appeals for help in the weeks after their daughter's disappearance.
This may be the the most logical explanation for a child vanishing without trace, as Madeleine did.
:: Accident
Madeleine woke up and went looking for her parents, opened the unlocked patio doors and walked out of the apartment, down the hill and fell into a big roadworks pit where she died or was knocked unconscious and was not spotted when the hole was filled in the next morning.
This theory assumes Madeleine, who was nearly four, would have been able to open the curtains, slide open the patio door and then shut the curtains and door behind her - as well as open and shut the garden gate to the road.
If she went looking for her parents it's likely she would have followed the route down the hill but, instead of continuing towards the roadworks, turned into the pool complex where they were eating. It was a journey she had taken regularly and in the dark street she would probably have been attracted by the light and noise.
Other accident scenarios suggest she walked out and was hit and killed by a car, whose driver panicked and disposed of her body. Or, she wandered off and squeezed herself into some remote, small place and couldn't get out or climbed into a well and drowned.
