Detectives hunting for Madeleine McCann have said for the first time that their investigation is focusing on the theory that she is dead.

Kate and Gerry McCann are believed to have been told yesterday morning that police now fear that their daughter was killed on the night she disappeared, 104 days ago.

The couple, from Rothley, Leicestershire, were assured that they are not suspects but a police spokesman refused to rule out the British friends who had been with them in Portugal.

Inspector Olegário Sousa, of the Polícia Judiciária (PJ), said: “The possibility of Madeleine’s death is the one that we are paying more attention to. However, none of the other possibilities is closed.”

Police have previously insisted that they had no evidence that Madeleine was dead, although they acknowledged on Saturday that she could have been been killed.

After analysing the evidence collected during a two-week review of their investigation, detectives concluded in the past few days that Madeleine was most likely to be dead. They have found no trace of Madeleine since she disappeared from the bedroom of her holiday apartment in Praia da Luz, Portugal. Inspector Sousa said: “The investigation has been collecting elements, analysing it, trying to get evidence and, at a certain point, this possibility, together with the lack of more strong evidence from the others . . . started to appear more consistent.”

He declined to provide further details, out of respect for Mr and Mrs McCann and on the ground that Portuguese secrecy laws forbid discussing details of continuing investigations.

However, Mr Sousa said that two sniffer dogs brought from Britain last month had uncovered new evidence in Madeleine’s bedroom that had been missed in earlier forensic science tests of apartment.

The traces, which were not visible to the naked eye, were sent for testing at the headquarters of the Forensic Science Service in Birmingham. The first set of results from the tests is believed to have already been sent to Portugal.

Mr Sousa emphasised again that police were not linking Mr and Mrs McCann to their daughter’s disappearance. “We said, again and again, until now the parents are not suspects,” he said.

His comments come after a week of lurid speculation in Portugal that Mr and Mrs McCann were responsible for their daughter’s death, shortly before her fourth birthday.

However, Mr Sousa refused to rule out the three British couples and the single woman who had stayed with the McCanns at the Ocean Club resort.

He told the SIC television channel: “Every time somebody is considered a suspect, he must have the status of ‘arguido’ [official suspect]. Until now, in this inquiry, there is one arguido and several witnesses.”

The Times revealed last week that the only arguido in the case, Robert Murat, 33, is set to be cleared after police failed to find sufficient evidence to charge him.

The announcement that police now believe Madeleine is dead follows an interview with Mrs McCann, in which she described the situation as “the worst kind of limbo”.

Mrs McCann, 38, a locum GP, said: “Gerry and I have spoken about this and in our heart of hearts we’d both rather know — even if knowing means we have to face the terrible truth that Madeleine might be dead. We both need to know.”

Mr McCann, 39, a consultant cardiologist, wrote in his blog yesterday that the couple were “waiting, like everyone else, for the next development in the police investigation”.

“We are still optimistic that there will be a breakthrough. In the meantime however, little has changed for Kate and I,” he said. “We will not give up hope until Madeleine is found and we will not stop searching for her.”

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