PORTUGUESE police tried to pressurise Kate McCann into admitting killing her daughter Madeleine by repeatedly showing her video footage of sniffer dogs allegedly finding the scent of a body in the family's hire car.

During 16 hours of interrogation she was shown the footage of the dogs clambering over the Renault Scenic car in the hope that she would break down and confess. She was yesterday said to be distraught and exhausted by the ordeal.

The dogs' reaction was a key reason why the police suspect her of killing Madeleine. Officers told Kate they had found her daughter's DNA in the car even though it was hired three weeks after her disappearance.

Kate and her husband Gerry are said to be mortified that the investigation team — with whom they have co-operated throughout — have apparently turned against them. "We are being absolutely stitched up," Gerry told a friend. "We are completely f*****. We should have seen this coming weeks ago and gone back to Britain."

Police hoped to force a confession from Kate after she was formally declared a suspect on Friday and subjected to further questioning.

Jon Corner, a friend of the family, said: "They kept coming back to the hire car and kept showing Kate the video of sniffer dogs. They also told her that Madeleine's DNA was found in the car."

Another friend said: "The suggestion being put to Kate was that if she had somehow killed Madeleine in an accident, then used a hire car to dispose of the body three weeks later, she should confess and the judge would look at it in a lenient light and offer three to four years in jail. It's absolute nonsense."

As it emerged that the family are considering approaching David Miliband, the foreign secretary, Portuguese detectives last night faced questions about the value of the evidence which they hoped would force Kate to break down. The family claim it is ambiguous and flawed.

They were supported by British forensic scientists who have also been surprised by aspects of the investigation. They said that the rental car — still in the possession of the McCanns — would have been automatically impounded as a central piece of evidence if it was a British police inquiry. The family point out that Kate has carried Cuddle Cat, Madeleine's soft toy, since her disappearance, which could explain the presence of her DNA in the rental car. British forensic experts also said that footage of agitated dogs would be of limited value in the law courts.

A Leicestershire police official is said to have told Gerry that the sniffer dog alone was not sufficient to consider someone a suspect, but was usually used as a basis for further intelligence gathering.

The Portuguese investigation team will face severe criticism from the McCanns' family and friends if it stakes its case solely on its forensic work. "The crime scene was completely desecrated after Madeleine's disappearance," said Philomena McCann, Gerry's sister.

"Literally hundreds of people went in that apartment after Madeleine was abducted. It was pandemonium. It was at least two days before any sort of fingerprinting was done."

The police are unlikely to change the focus of their investigation. Portuguese newspapers were yesterday reporting that Kate was suspected of homicide, negligence and "preventing the corpse from being found". According to the reports, one police theory is that Kate accidentally gave Madeleine a fatal dose of sedatives. It has been strenuously denied by representatives of the McCanns that they gave any of their children sedatives. There was also speculation that Kate could face charges within a few days. Despite the threat of an impending prosecution, the McCanns are now anxious to return home. A court could put restrictions on their movements and the couple have said they will not leave without consulting the police.

"They really miss Madeleine and they really want everyone to concentrate on the fact that she is still missing," said a friend. "They feel that after the events of the past few days no one is carrying on with the search." The McCanns have been liaising with the Foreign Office in the hope that Miliband would be able to obtain more information on the state of the police inquiry.

Miliband said yesterday: "Firstly we must remember above all else that this is about a missing girl. Secondly, obviously we have been and will continue to give extensive consular support to the family. And thirdly, in respect of the independent judicial process, we must let that take its course."

The declaration of the couple as suspects will raise questions about the future care of the two-year-old twins if they are charged. It is understood that other members of the family would act as guardians if the authorities moved to take custody of the twins.

Kate and Gerry were interviewed by police on Thursday and Friday after detectives are thought to have obtained the results of tests conducted by

the Forensic Science Service in Britain. It is understood that Kate faced questions over whether she had given her daughter sedatives, why Madeleine's DNA was found on her clothing and in the rental car and why sniffer dogs found the scent of a body on her clothes and in the rental car.

Hugh White, a Home Office pathologist, said he could not understand why the car was held by the police for just two days. "In this country the car would have been stripped down into tiny pieces and the forensics team would be crawling all over it," he said. Other forensic scientists said the information revealed so far was far from conclusive. Keith Borer, a retired forensic scientist, said: "What they seem to have found makes good questions for a police interview, but evidentially it seems pretty weak."