The McCanns ‘refused to answer 40 key questions’ during a police interview after being made official suspects, it was reported yesterday. Here our correspondent looks at some of the crucial riddles of the past four months

David Brown in Praia da Luz

What happened in the four hours before Madeleine was reported missing?

Kate and Gerry McCann claim that while they dined at a restaurant with friends regular checks were made on Madeleine and their two-year-old twins, Sean and Amelie, at their nearby holiday apartment. Mr McCann told police he saw his daughter asleep at about 9pm. A friend, Matthew Oldfield, entered the apartment at about 9.30pm but did not look in the bedroom Madeleine and the twins were sharing.

It is not known if anyone apart from Mr and Mrs McCann saw Madeleine alive between 6pm and 10pm, when she was reported missing by her mother. The timing is crucial but would be only circumstantial evidence in any prosecution. Although a small child could be killed quickly it would take time to hide a body so that it was not discovered in the biggest search in Portuguese history.

Why did Kate McCann cry out “They’ve taken her?” when she discovered Madeleine missing?

Portuguese police are reported to find it suspicious that Mrs McCann immediately believed that more than one person had taken her daughter. This could suggest that she knew who had taken Madeleine, perhaps people who thought they were helping Mrs McCann by removing her daughter’s body.

Alternatively, it could be an off-the-cuff remark by an hysterical mother or perhaps was misheard or misunderstood in the confusion of the night.

What were the movements of the McCann’s friends on the night Madeleine disappeared?

The McCann family had stayed at the Ocean Club resort with three other British couples and their five children, and a single woman. Russell O’Brien, a doctor from Exeter, left the restaurant for half an hour to look after his own daughter, returning shortly before Madeleine was reported missing.

His wife, Jane Tanner, was the only witness to report a man carrying away child from the McCann’s apartments. There is confusion about when members of the party arrived at the tapas restaurant and left to check on their own sleeping children.

How much alcohol did the McCanns and their friends drink on the evening Madeleine disappeared?

Kate and Gerry McCann and their friends are reported to have told detectives they shared four bottles of wine, with another two barely touched before Madeleine was discovered missing.

However, it is claimed detectives have recovered a bill showing they downed eight bottles of red wine and six white during the afternoon and evening.

Why was Madeleine’s bedroom window and shutter open?

Kate and Gerry McCann told police that the window shutter in Madeleine’s bedroom, which could not been seen from the restaurant, had been forced open.

Police tests showed the heavy metal shutter had not been forced up from the outside, so must have been pulled open from inside the room. Assuming that the abductor entered through the apartment’s unlocked patio windows, why would he or she not leave by the same way or the use the front door?

Or was the window opened to make it appear as if an intruder had used it to enter the bedroom?

Why did Madeleine’s sister and brother sleep through her “abduction”?

Sean and Amelie were heavy sleepers who were not disturbed by their sister’s abduction, claim their parents. However, they also slept through their mother’s hysterical response to Madeleine’s disappearance and the presence of dozens of people who joined the search before being carried out by a female police officer. Kate and Gerry McCann have strenuously denied sedating their daughter.

Why were the McCanns allowed to leave Portugal if they are suspects?

The Portuguese authorities allowed the McCanns to return to the UK after they agreed to reside only at their home in Rothley and to return for further questioning if necessary.

Portugese law states that after someone is declared a suspect, police have eight months to conclude the investigation into that individual. If they require further time officers can apply to the courts for a four-month extension.

If the McCanns refused to comply with a request to return to the Algarve for interview, Portuguese police could issue a European Arrest Warrant under which extradition can be carried out within six weeks.

All parties have strenuously denied any wrongdoing.