The McCanns: Unbelievable truth or unimaginable nightmare?

Kate and Gerry McCann returned to Britain six days ago with the tide of public opinion turning against them. The huge outpouring of sympathy and support that followed the disappearance of their three-year-old daughter Madeleine in Portugal on 3 May had given way to shock and confusion for many of their supporters when the couple were named as formal suspects by police.

They flew back to Rothley in Leicestershire with friends claiming they were being framed. But while many people could believe the McCanns were going through hell, others suddenly felt able to express rage.

A BBC Radio 5 Live phone-in on the McCanns on Monday was abandoned after a flood of critical calls. The Leicester Mercury had to withdraw a website opinion page "bombarded" with "nasty, spiteful and defamatory" comments. More than 17,000 people signed an online petition calling for Leicestershire social services to investigate the McCanns for leaving their children sleeping alone in Praia da Luz that night. Social workers did go to see them, but had been invited.

Tabloid newspapers that campaigned to Find Maddie started to run brutal headlines like: "Madeleine Was Killed By Sleeping Pills". But there was no definite proof of that at all.

The prosecutor in the Algarve passed a 4,000-page file on the case to judge Pedro Miguel dos Anjos Frias, who has until Thursday to decide what happens next. The McCanns, both 39, could be charged. Their bail restrictions could be tightened, possibly forcing them to return to Portugal. The police could be given more time. Or the whole thing could be dropped.

The leaked police case appears to be that Kate McCann accidentally killed her daughter with an overdose, and the couple then conspired to cover it up. They would have had to show extraordinary nerve in hiding the body, making repeated appeals for Madeleine's return then moving her corpse again when the world was watching almost their every move. If the accusations are false, and the McCanns innocent, then they are trapped in an unimaginable nightmare.

Which is it? As they await the decision of the judge, protesting their innocence and continuing to call for the hunt for their daughter to be stepped up again, here is what we now really know – and what we still don't.

What may the charges be?

Friends of Kate McCann say police told her they believed her guilty of "accidental homicide". Gerry McCann is said to be under suspicion of helping his wife hide the death. That could make him an accessory or lead to a charge of perverting the course of justice.

What evidence is there?

Without a body or a confession, detectives have tried to piece together a patchwork of clues about what happened that night at the Mark Warner Ocean Club resort. The McCanns say they left her sleeping with her two-year-old twin brother and sister in the apartment while they dined at a tapas bar 70 yards away with friends. Mr McCann checked on them at 9pm. A friend who was away from the dinner table for a while says she saw a man carrying a child wrapped in a blanket near the apartment at around 9.15pm, but thought nothing of it. Another friend listened outside the room at 9.30pm. Kate McCann returned to the apartment at 10pm then raised the alarm. Not all the alleged evidence against her has become public – far from it – but that which has arises from forensic investigations of the flat and a car the couple hired 25 days after the disappearance.

What was in the hire car?

The silver Renault Scenic was examined by a sniffer dog trained to detect any scent of a corpse, and police sources say they saw the dog "going crazy". Mrs McCann has said that as a GP she was with corpses before the holiday, so traces of them may still have been on her clothes. But the big breakthrough, the media claimed, was Madeleine's hair and bodily fluids being

found in the car.

How could hair be there?

If there was not much then it could have been gathered on a brush or even clothes before Madeleine's death and transferred to the car when the McCanns moved from the apartment to a rented villa. But there are strong indications from the police that there was an "unusual" amount of hair under the carpet in the boot, where the spare tyre goes, which they say could mean the young girl's body was hidden there before disposal. The tests will reveal whether the hair was torn out – by a brush, for example – or fell out, potentially as a result of death.

What could body fluids be?

Sweat, possibly, or urine from a potty, which would prove nothing. But experts say decomposing bodies give off certain kinds of fluids. Their presence would appear to place Madeleine in the vehicle after death. But as a reputable police source said, that "would not prove homicide, just that the body of the girl had been transported in the car".

What was in the flat?

One of the cadaver-sniffing dogs detected traces of a corpse there, on a Bible and Mrs McCann's clothes. Reports also say the scent formed a trail down to a local beach. Another dog reportedly found blood in a spatter pattern by the windowsill. The chief of police in Portugal, Alipio Ribeiro, said: "Various analyses were received but none of those tests are that exact (giving 100 per cent certainty) so, in other words, we cannot say blood belongs to person A or person B."

Where did the samples go?

The Forensic Science Service in Birmingham. The first results were passed to Portuguese police last week, with more to come. There has been no official comment about tests or results.

Was there a DNA match?

The bodily fluids found in the car reportedly matched Madeleine's genetic profile by 88 per cent, which the Portuguese press called "conclusive". But Sir Alec Jeffreys, inventor of DNA fingerprinting, said: "There are no genetic characters in Madeleine that are not found in at least one other member of the family. So when you have an incomplete DNA profile, that could raise a potential problem... given all other members of that family would have been in that car."

Could the samples reveal she was overdosed?

The newspaper France Soir reported that toxicology tests on the bodily fluid showed Madeleine to have died from an overdose of sleeping pills, but this has not been confirmed. Alan Baker of the forensic science company Bericon said: "These samples are likely to be far from ideal. If it is just a smear or dried deposit you would detect the drug but not how much."

What could be proved by testing the "cuddle cat"?

Very little, it would seem. The pink toy that Mrs McCann carries is her constant reminder of Madeleine. Reports suggest she washed the "cuddle cat" because it had become dirty and smelled of sun cream. At least one police officer has told reporters he finds that strange. In any case, it is obvious that Madeleine's DNA would be on her toy.

Does the search go on?

The police now appear to be looking for a body. Portuguese newspapers have reported that they will resume looking inside and around the church of Our Lady of Light in Praia da Luz where the McCanns attended services regularly.

What is in Kate's diary?

Her thoughts and feelings after 3 May, according to reports. The police have the original but under Portuguese law must apply to the judge for permission to use it. Detectives apparently believe the diary shows Mrs McCann had trouble coping with her three energetic children. However, it is not certain the diary could be used in court. Police also have Mr McCann's laptop.

What do the McCanns and/or their friends say?

They are innocent. The hunt for their daughter's true abductor has been neglected. Neither the flat nor the hire car were sealed off to protect the forensic evidence. Police should look again at the other formal suspect, Robert Murat. And detectives are ignoring the key claim about the man seen carrying a child. The battle to keep Madeleine in the public mind appears to have become an effort to rebut police leaks. Or alternatively, if you think they did it, to undermine the investigation.