The investigative journalist who uncovered and exposed paedophile Jimmy Savile for his evil crimes has a new working theory about what happened to Madeleine McCann.

The 3-year-old disappeared from her parents’ apartment in Praia da Luz, Portugal, on May 3, 2007, leading to a 15-year investigation and manhunt to find out what happened.

Parents Gerry and Kate McCann were eating at a tapas restaurant nearby while Maddie and her siblings were left alone in their apartment.

When Kate returned to check on the children, Maddie was gone.

Despite paedophile Christian Brueckner being the latest suspect, investigative journalist Mark Williams-Thomas has his own theory of the last movements and fate of Maddie.

Madeleine McCann disappeared in Praia da Luz, Portugal on May 3, 2007.

Speaking on the Extraordinary Lives podcast, Williams-Thomas, a former police officer, says after poring over evidence he has concluded Maddie will never be found and painted a likely theory of what happened.

The 52-year-old said the most likely scenario is that Maddie woke up in the middle of the night and, wondering where her parents were, went to look for them.

“I brought all the information together, read all the police files, I spoke to all those key witnesses around there, and I had a contact via one person removed from the family, and so I was able to pull all this information together.

“My conclusion is that on that night of Madeleine’s disappearance, she woke up, looking for mum and dad. She’d been told that if she were to wake up, the parents were only in the tapas bar, which was just across the courtyard.

“What we do know is that her brother and sister had woken up on the previous nights a number of times, and I suspect as a result of that, Madeleine thought, ‘well, where is mum and dad?’, as they’d been out on those previous nights as well.”

He went on: “So I believe she woke up, she left the apartment, we know the apartment was insecure, the back patio door was open to allow some flow of air, it was very hot.”

Mark Williams-Thomas is an investigative journalist who helped uncover Jimmy Savile's horrific crimes. Photo / Ladbible Podcast

Williams-Thomas who was invited to speak at a conference hosted by the FBI, also cited another two cases saying he believes Maddie would have been snatched and killed within “72 hours”.

“Evidence tells us, through the FBI child abduction manual, which is very detailed and very good, because they’ve got 10 times the child abductions/stranger-child abductions as we’ve had in the UK, that she would have been dead within 72 hours.”

He went on to say he think it is “sadly probably unlikely” investigators will ever find out what really happened to her.

“But I always use the caveat that we have to remain positive that one day we will.”

Williams-Thomas began investigating the Jimmy Savile case in late 2011, after being informed that Savile was investigated by Surrey police in the late 2000s. On October 3, 2012, Williams-Thomas presented the Exposure documentary The Other Side of Jimmy Savile on ITV, in which five women stated that they had been sexually abused by Savile as teenagers.

By late October 2012, the scandal had resulted in inquiries or reviews at the BBC, within the National Health Service, the Crown Prosecution Service, and the Department of Health.

In June 2014, investigations into Savile’s activities at 28 NHS hospitals, including Leeds General Infirmary and Broadmoor psychiatric hospital, concluded that he had sexually assaulted staff and patients aged between 5 and 75 over several decades.

Savile died in October, 2011.