A British scientist warned DNA tests on a sample from Kate and Gerry McCanns’ hire car were inconclusive just days before the couple were made suspects, official police files have revealed.
In an email John Lowe, from the major incidents team at the Birmingham-based Forensic Science Service (FSS), said it was impossible to conclude whether the material came from their daughter Madeleine.
Four days later Portuguese detectives named the McCanns “arguidos”, or suspects, , citing DNA evidence as grounds for suspicions.
The revelation came to light after the police files from the exhaustive inquiry, which lasted over 14 months, were made public yesterday.
Journalists were handed DVDs containing copies of thousands of pages of evidence 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 the email written by Mr Lowe to Detective Superintendent Stuart Prior, head of the British side of the investigation.
In it the scientist reported that a sample from the boot of the McCanns’ Renault Scenic hire car, which they rented 24 days after Madeleine went missing, contained 15 out of 19 of the young girl’s 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”.
Mr Lowe wrote: “Let’s look at the question that is being asked: ‘Is there DNA from Madeleine on the swab?’ It would be very simple to say ‘yes’ simply because of the number of components within the result that are also in her reference sample.
“What we need to consider, as scientists, is whether the match is genuine – because Madeleine has deposited DNA as a result of being in the car or whether Madeleine merely appears to match the result by chance.”
The expert noted that the components of the missing girl’s DNA profile were not unique to her – in fact some of them were present among FSS scientists, including himself.
He concluded: “We cannot answer the question: is the match genuine, or is it a chance match.”
Lawyers for the McCanns, both 40, from Rothley, Leicestershire, were formally given access to the documents last week.