A retired private investigator who worked in the case of missing Madeleine McCann, a British 3-year-old who disappeared over a decade ago while on vacation with her family in Portugal, is convinced Maddie is still alive and being held captive.

David Edgar, a retired Detective Inspector who worked for the family on the missing persons case for three years, and shared his findings with London’s Metropolitan Police Service in 2011, told The Sun that he believes Maddie may still be in Portugal, possibly being held against her will.

Edgar told the news outlet that he long believes Maddie may have been kidnapped as part of a sex slave operation, and that it is possible she is being held in a concealed residence or a den, likely in Portugal.

“There is every possibility that Madeleine is still alive and could be being hidden somewhere and having no idea even who she is and that she is at the centre of a worldwide hunt for her,” Edgar told The Sun.

Maddie was three years old when she vanished from a hotel room where she was sleeping with her siblings while her parents were at a restaurant on the resort property. Authorities have never made an arrest in the case, although some, including a police officer who worked on the investigation in its early days, have publicly suspected Maddie’s parents Kate and Gerry of being involved. The parents have steadfastly maintained their innocence through the years and have worked to keep the investigation active.

Edgar told The Sun that he was hampered in pursuing his theory because he was a private investigator and not a member of the law enforcement teams investigating the case.

“Not for want of trying but as a private investigator I was faced with certain restrictions and stumbling blocks unlike the official authorities,” Edgar said.

But now Edgar says he believes a new tip given to police may have come from someone who knew about the kidnapping.

“I’ve always thought that whoever is responsible will have confided in someone else,” Edgar told the newspaper. “They usually do and it is very rare that they don’t even if it takes years.”

“Now we’re approaching the 12th year, that’s a significant time but I think she could still be alive and someone is protecting her captors. Someone knows what happened and it’s time they came forward, may be they have and officers are waiting for a confession. It happens.”

According to the report, investigators recently told Maddie’s parents that they are working on two “specific and active lines of inquiry,” suggesting a new lead in the case.

A spokesperson for Scotland Yard reportedly declined to comment to The Sun, saying, “We cannot give a running commentary while there is an ongoing investigation.”