On Monday Panorama goes to the heart of the question that has troubled the UK since the disappearance of Madeleine McCann just over six months ago.
Why have her parents, Kate and Gerry, found it so hard to shake off the suspicion that they somehow had a role in her going missing?
Panorama: The Mystery of Madeleine McCann, BBC One Monday 19 November 2007
In an hour-long special Richard Bilton talks to those who had direct contact with the McCanns at the time and travels to Portugal to question those close to the case in an attempt to separate fact from fiction.
Lack of clues
He attempts to nail some of the wild claims made against the couple and question what remains of the evidence.
Madeleine's parents have been in the glare of the public eye since Madeleine vanished from their apartment in Praia da Luz, Portugal, on 3 May.
Thanks to a high-profile campaign run by the McCann family, Madeleine's face has rarely been out of the public consciousness.
But because of the lack of clues, and the Portuguese police's secrecy laws, there are few firm details about what happened the night Madeleine went missing and the subsequent investigation.
This is what we know so far.
Madeleine McCann went missing from her family's holiday apartment at the Ocean Club, in Praia da Luz, on 3 May.
She was holidaying with her parents and her younger twin siblings.
Mrs McCann is understood to have told police that after tucking the children up in bed Madeleine - who was wearing pink pyjamas with the words "Sleepy Eeyore" on them - said: "Mummy, I've had the best day ever. I'm having lots and lots of fun."
It is known Mr and Mrs McCann then went for dinner with a group of friends, at a tapas restaurant 100 yards from the apartment.
Their party included friends and fellow holiday-makers Dr Matthew Oldfield, Rachael Oldfield, Dr Russell O'Brien, and Dr Fiona Payne.
Leaks from the investigation suggest the McCanns arrived for dinner at 2040 local time that evening, according to their friends.
At 2105 Mr McCann went to check on the children, followed by Dr Oldfield at 2130, they said.
Mrs McCann told police that when she went to the apartment at 2200 she found the outside shutter and window to Madeleine's room had been opened and her daughter was missing.
Mrs McCann said police were called within 10 minutes of finding her daughter gone. Guilhermino Encarnacao, director of the judicial police in the Faro region, said officers arrived within 10 minutes of being alerted, and an investigation unit began work within 30 minutes
The manager of the Mark Warner resort in Portugal, John Hill, said about 60 staff and guests at the complex searched until daybreak for the little girl, while police notified border police, Spanish police and airports.
They were joined in their hunt by hundreds of volunteers in the following days.
3 May - Three-year-old Madeleine McCann goes missing from her family's apartment in Praia da Luz.
5 May - As the search for Madeleine continues, her parents issue a statement to say they "cannot describe the anguish and despair" they are feeling at their daughter's disappearance.
12 May - Mr and Mrs McCann make a fresh appeal for help on their daughter's fourth birthday.
15 May - British-born Robert Murat is made an official suspect - or "arguido" - following a search of his mother's villa. Casa Liliana is 150 yards from the apartment where Madeleine went missing.
26 May - A description of a man seen on the night Madeleine went missing "carrying a child or an object that could have been taken as a child" is issued by police.
30 May - The McCanns meet the Pope at a general audience in Rome at the start of a "European tour" to raise awareness of Madeleine's disappearance.
6 June - A German reporter asks the McCanns how they feel about the fact that "more and more people seem to be pointing the finger" at them, during a press conference in Berlin.
12 June - Mr and Mrs McCann arrive back in Portugal following their European tour.
17 June - Chief Inspector Olegario Sousa admits vital forensic clues may have been destroyed in the hours after Madeleine's disappearance, as the scene was not protected properly.
10 July - Formal suspect Robert Murat re-questioned
Late July - British sniffer dogs fly out to Portugal. Keela, who can detect minute quantities of blood, and Eddie, who is trained to detect dead bodies, work in the apartment and several cars, including the hire car the McCanns rented 25 days after Madeleine disappeared.
6 August - Police fail to find any new evidence after a search at the home of Mr Murat following a two-day search, the BBC understands.
7 August - Forensic tests are carried out in a Birmingham lab on suspected traces of blood found by sniffer dogs in Madeleine's apartment.
11 August - Police in Portugal acknowledge for the first time that, in light of new evidence, Madeleine may be dead. Chief Inspector Sousa adds that Mr and Mrs McCann are not being considered as suspects following newspaper speculation that they were under suspicion.
24 August - Police say they still have doubts over how Madeleine disappeared and whether she will ever be found.
31 August - The McCanns launch a libel action against Portuguese newspaper Tal & Qual which claimed "police believe" they killed their daughter. The McCanns say they are "deeply hurt" by the allegations.
6 September - Portuguese police interview Kate McCann for 11 hours as a witness in the presence of her lawyer. Separately, Portuguese detectives confirm they have the partial results of forensic tests by a UK laboratory.
7 September - Madeleine's mother is declared an official suspect and fears she could be charged, friends say. Gerry McCann is also named as a formal suspect following more questioning. Later, a family representative says officers believe they have found traces of Madeleine's blood in the McCanns' car, hired 25 days after she vanished.
9 September - Kate and Gerry McCann return home to Rothley, Leics.
10 September - Police papers detailing the inquiry into Madeleine's disappearance are passed to Algarve-based prosecutor, Jose Cunha de Magalhaes e Meneses. In Leicestershire, police and social services meet to discuss the case.
11 September - In his internet blog, Gerry McCann says he and his wife Kate face an "unbearable" situation.
Portuguese police play down reports that DNA evidence with a 100% match to Madeleine was found in her parents' hire car.
A statement is made outside the prosecutor's office in Portimao, saying he had received the files detailing the inquiry into Madeleine's disappearance and decided they should go before an instructional judge.
The judge has 10 days to make a decision on the files' contents.
19 September - Portuguese prosecutors rule there is "no new evidence" in police files to justify re-questioning Gerry and Kate McCann.
26 September - A photograph taken by a Spanish tourist in Morocco is examined by experts, amid suggestions a girl in the picture could be Madeleine. Reporters later claim that the girl is in fact a Moroccan five-year-old.
What exactly is the DNA evidence, currently being examined in the laboratory in Birmingham? Senior sources said to be linked to the investigation have told Portuguese journalists that they discovered "bodily fluids" - not blood - with an 88% match to Madeleine's genetic profile in the car's boot.
One source has apparently said police also found so much of the girl's hair in the car that it could not have been transferred from a blanket or clothes, and must have come directly from her body. The Portuguese police have refused to comment on any details of their investigation.
How might Madeleine's DNA have got into the McCanns' hire car? Allan Scott, a lecturer at the University of Central Lancashire's School of Forensic and Investigative Sciences, says cross-contamination - or so-called "secondary transfer" - could explain the alleged discovery of Madeleine's blood in the family's hire car.