Experts question DNA evidence claims in McCann case

British experts cast fresh doubt today over claims relating to the forensic evidence at the heart of the investigation into the disappearance of Madeleine McCann.

As Gerry and Kate McCann spent their first full day at home after their return to Britain yesterday, yet more claims relating to the case were being reported in Portugal.

Portuguese newspapers said “biological fluids” with an 80% match of the toddler’s DNA were found underneath the upholstery in the boot of the McCanns’ rented Renault Scenic.

There has also been growing speculation in recent weeks that forensic samples recovered from the family’s apartment in Praia da Luz and in the car indicated the presence of her dead body.

But according to Allan Scott, a lecturer at the University of Central Lancashire’s School of Forensic and Investigative Sciences, both claims are – at the very least – questionable.

He said today: “I have been speaking to DNA experts at the university – and these are some of the top DNA specialists – and we believe you cannot tell if DNA is from a dead subject.

“It is about your blood group, which does not change because you have died. A person’s DNA profile does not change just because they die.

“You can tell if the DNA has degraded but that could happen fairly quickly depending on the environment, if for example it is getting baked in the sun.

“It may be possible to see that a DNA sample has degraded because of where it was or the length of time between it being deposited and recovered but that does not tell you if the person is dead or alive.”

Moving onto the idea of an 80% DNA match, he added: “I cannot understand where this idea has come from. If they say it is Madeleine’s blood full-stop, it is a one in a billion chance of not being her blood but if it is an 80% match, I don’t know.”

The expert explained that the key factor is whether forensic scientists had examined the entire DNA thread, or just one section – such as that genetically inherited from one parent.

He said: “Normal DNA is 25% the person’s father, 25% the mother and 50% the individual’s own.

The McCann twins, because one is male and one is female, will have different DNA even though they are twins.

“The mitochondrial DNA follows down the female line. It is not as accurate as other forms of DNA comparison. You can only really use it for exclusion.

“If you are looking at the mitochondrial DNA, there is a one in a hundred chance it might not be a match, compared to one in a billion. Other methods of comparison, such as looking at the copy number or SGM+, will examine the whole strand of DNA so are more accurate.”

Sniffer dogs provided by British police were also used in the police investigation and were claimed to have “smelt death” in the family’s apartment and the hire car.

Mr Scott, a career crime scene investigator and one-time head of scenes of crime at Merseyside Police, accepts this is a possibility, but again says there is no way to be certain.

He said: “I have used one in the past and the dog did detect that a cadaver was there but it is only an indication. It’s not as if there is a way you can get a dog in the witness box and ask him to raise his right paw.

“In that case, we still have not found the missing person, who was a drug dealer.

“You can put them on the front of a small boat in a lake or river and they can actually detect decomposition gases. They’re fairly sensitive. We are not talking about ordinary police Alsatians, we are talking about dogs that are good scent tracking dogs, like Spaniels.”

Alan Baker, a forensic scientist who has given expert evidence on the subject of DNA in court cases, agreed it was impossible to say from DNA if an individual was dead or alive.

He said: “With DNA, you cannot tell if someone is alive or dead or say exactly where it has come from. It depends on the nature of the sample, whether it is blood, sweat, hair follicles or whatever.

“DNA itself would not tell you if that person is dead or alive. If it was associated with bone fragments or a piece of tissue, that is another story.”

He also questioned the 80% match claim, saying scientists usually spoke in terms of one in a million or billion chances of a match rather than in percentages.

“It might be a different case of presenting that or it might be that someone has done some crude maths and said, for example that if 16 of 20 elements match, then that is 80%,” he said.

And he also pointed out the huge gaps in terms of what is known about the evidence in the case, which could hold the key to what has happened to the four-year-old.

He said: “My view is that the science itself is entirely reliable. The issue is what is missing and that is what stops the forensic scientists from going into a lot more detail.

“The difficulty is getting at what is in that forensic statement. In the UK, we would not know about the DNA evidence or the connections which has prompted all this speculation about how significant it is.

“It may be that a small part of the jigsaw is one that would be helpful to the Portuguese police. But I am intrigued what it could be because the crime scene does not appear to have been searched properly.”