A phenomenon called noble cause corruption can sometimes unintentionally bias police investigations and lead to miscarriages of justice, according to a high-profile American defence lawyer.

Veteran attorney David S. Rudolf became something of a digital age folk hero after appearing in Netflix show The Staircase , a true crime documentary detailing the murder trial of US author Michael Peterson , who was found guilty of killing his wife but later had his conviction overturned.

Speaking in episode eight of Maddie , Nine.com.au's podcast investigation into Madeleine McCann's disappearance, Rudolf explained why, generally, it can sometimes be hard for police to back away from a line of inquiry that later appears to be flawed or wrong.

"The larger problem is not the kind of corruption that we normally think about but what ... is called noble cause corruption," Rudolf said.

"And that's the kind of corruption that occurs when the police believe in a particular theory, and take steps that are extra-judicial in order to prove their theory."

Rudolf explained that police and judges, like all human beings, can suffer from confirmation bias - a psychological dynamic where people tend to ignore or emphasise relevant facts depending on their beliefs.

"We all to a greater or lesser extent suffer from tunnel vision," he said.

"Police officers and even judges [can have] a certain arrogance about their ability to determine what actually happened, and then fall guilty to tunnel vision and confirmation bias."

Michael Peterson, left, reacts after being found guilty of murdering his wife in October 2003. At right is his attorney David Rudolf. Novelist and onetime mayoral candidate Michael Peterson was found guilty of murdering his wife, whose body was found in a pool of blood at the bottom of a staircase in their home. His conviction was later overturned. (AAP)

In 2017, a senior London Metropolitan Police figure rejected claims Operation Grange detectives had a "closed mind" about scenarios which do not involve Madeleine McCann being abducted in May 2007.

Rudolf also offered his opinion on why Scotland Yard's Operation Grange , the $20 million, seven-year UK police investigation into the Madeleine mystery, have so far failed to take up an offer from one of the world's leading DNA scientists to solve a series of possibly case-changing DNA samples.

Following an investigation by Nine.com.au , US forensic scientist Dr Mark Perlin has made a formal offer to London Metropolitan Police to untangle 18 complex DNA samples at no cost. Those DNA samples, taken from the McCann holiday apartment and rental car, were ruled "inconclusive" in 2007 and are potentially loaded with vital clues about Madeleine's disappearance.

A former Scotland Yard homicide detective, Colin Sutton, has said solving those DNA samples could be a "gamechanger" for police . Two of the 18 DNA samples being sought for analysis by Dr Perlin were lifted from a rental car hired weeks after Madeleine vanished.

To date, Dr Perlin has had no response or acknowledgement from Scotland Yard.

Michael Peterson, right, is handcuffed by Durham Sheriff's officer Bryan Mister in2003 after being found guilty of first degree murder in the death of his wife, Kathleen Peterson. Defence attorney David Rudolf is standing to Mr Peterson's right. His conviction was later overturned. (AAP)

"The natural conclusion I think is what's the harm of doing the analysis? And if you don't want to do the analysis then perhaps what you're afraid of is that you'll be shown to have been wrong in your initial theory," Rudolf said, speaking about Operation Grange's apparent unwillingness so far to take up Dr Perlin's offer.

"And that's hard for people, you know. It's hard for people to admit they're wrong and it's hard for people to agree to testing that may show they're wrong. What it says to me is that whoever is resisting it is human and they're somewhat concerned that what they initially thought may not be the case."

Operation Grange detectives were first made aware of Dr Perlin's offer in March last year. Scotland Yard have been contacted several times since by Nine.com.au but refused to comment on Dr Perlin.

Dr Perlin, chief scientist at Cybergenetics, has confirmed to Nine.com.au he has not been contacted by anyone at Scotland Yard, including DCI Nicola Wall who heads up the investigation which was launched in 2011 and has cost taxpayers more than $20 million.

The UK Home Office is currently considering a request for further funding, believed to be $300,000, from Operation Grange to continue the investigation through to March 2020.

UK Prime Minister Theresa May and the Home Office both declined to comment on Dr Perlin's pro bono offer when approached by Nine.com.au .

In an earlier episode of Maddie , retired London Metropolitan Police detective Colin Sutton was asked what it could mean if Dr Perlin's analysis confirmed the presence of Madeleine's DNA in that rental car, a silver Renault Scenic.

"On that basis, that that car was hired by the McCanns three weeks after Madeleine disappeared, then it is a real game changer, isn't it? Because there is no way, according to information that we have, that she could have been in that car," said Sutton, who solved more than 30 murders, including catching English serial killer Levi Bellfield.

Cybergenetics chief scientist Dr Mark Perlin has pioneered tremendously powerful software to solve extremely complex DNA evidence. (Supplied / Credit: Andrew Rush)

"The big question then is how can her DNA get into that car three weeks after she disappeared?"

Dr Perlin said DNA transference could be a possible explanation if Madeleine's DNA is found to be present in the car, and would be something examined by police and forensic experts.

DNA analysis by Dr Perlin could also conclusively rule out Madeleine as ever having been in the car, helping to narrow the focus of the investigation, as well as shed light on some of the questions around the other DNA samples.

In a rare media briefing about Operation Grange in 2017, the now retired London Metropolitan Police Assistant Commissioner Mark Rowley was asked if Madeleine’s parents had ever been questioned under caution or considered suspects.

"The involvement of the parents, that was dealt with at the time by the original investigation by the Portuguese," Rowley replied.

"We had a look at all the material and we are happy that was all dealt with and there is no reason whatsoever to reopen that or start rumours that was a line of investigation."

During questioning, he fended off criticism Operation Grange and its investigative remit of a potential abduction appeared to have a "closed mind" to the possibility of the involvement of someone known to the family, an accident or the girl walking out of the apartment.

Kate and Gerry McCann, both doctors from Rothley, Leicestershire, have strenuously denied they were involved in the disappearance of their daughter. Nine.com.au does not suggest any involvement on their part.

Mr and Mrs McCann left Madeleine and their two other children alone while they ate dinner at a nearby restaurant with a group of friends.

They believed an intruder struck while they were out , taking Madeleine from her bed.

Aged three when she vanished, Madeleine would turn 16 in 2019.

Maddie podcast investigation of Madeleine McCann disappearance. (Nine)