The parents of Madeleine McCann were made official suspects in their daughter Madeleine's disappearance despite a warning that there was no conclusive DNA evidence against them, official police files have revealed.

Portuguese police named Kate and Gerry McCann as arguidos on September 7, four days after the Birmingham-based Forensic Science Service (FSS) laboratory said it was impossible to conclude whether material found by officers came from the toddler.

The revelation came to light after the mammoth police files from the inquiry, which lasted over 14 months, were formally made public yesterday.

Previously unseen official pictures from inside the apartment where the McCanns were staying when Madeleine went missing - including a photograph of the bed in which she had been sleeping - were among other items released under Portuguese law after the lifting of the period of judicial secrecy in the case.

Portuguese police files also reveal Kate McCann refused to answer 48 questions put to her by Portuguese detectives after she was made a suspect in Madeleine's disappearance.

Journalists were handed DVDs containing copies of thousands of pages of evidence from the case outside the courthouse in the Algarve town of Portimao.

The dossier includes details of the lines of inquiry pursued by detectives, forensic reports, witness statements and transcripts of interviews with the McCanns.

Among the files is an e-mail written by John Lowe, a scientist with the FSS major incidents team, to Detective Superintendent Stuart Prior, head of the British side of the investigation.

In it Mr Lowe reported that a sample from the boot of the McCanns' hire car, which they rented 24 days after Madeleine went missing, contained 15 out of 19 of her DNA components.

But he cautioned that this result - based on the controversial "low copy number" DNA analysis technique which uses very small samples - was "too complex for meaningful interpretation or inclusion".

He also stressed that low copy number analysis could not determine when or how the DNA was deposited, what body fluid it came from and whether a crime was committed.

The papers reveal Mrs McCann used her right as an "arguido", or formal suspect, to remain silent during this section of her interview on September 7 last year.

Officers quizzed her about everything from her medical specialism and Madeleine's behaviour, to whether she had any responsibility for the little girl's vanishing.

The final unanswered question was: Did you have any responsibility or intervention in your daughter's disappearance?

The files show that the only question Mrs McCann did answer was: "Are you aware that in not answering the questions you are jeopardising the investigation, which seeks to discover what happened to your daughter?"

She replied: "Yes, if that's what the investigation thinks."

Mrs McCann has always strenuously denied any involvement in Madeleine's disappearance and her arguido status was lifted on July 21.

Madeleine has not been seen since she vanished from her family's holiday apartment in the Algarve resort of Praia da Luz, on May 3, last year, a few days before her fourth birthday, while her parents were having dinner with friends at a nearby restaurant in the town.

Lawyers for the McCanns were formally given access to the files last week and are studying the dossier for fresh leads that the couple's private detectives, or detectives in other countries, may be asked to follow up in the family's own search for their daughter.