It’s been more than 10 years since British toddler Madeleine McCann disappeared during a family vacation in Portugal – but investigators apparently haven’t stopped searching. Detectives were now set to travel to Bulgaria to speak to the widow of a sex offender who may have information, according to the Independent.

Madeleine disappeared in May 2007 after her parents left her alone with her 2-year-old twin siblings inside a vacation rental apartment in Praia da Luz while they went out to dinner.

The woman, apparently dubbed “the woman in purple,” was allegedly seen by an eyewitness staring at the apartment block near where the McCanns were staying when 3-year-old Madeleine disappeared. The woman was reportedly married to a convicted sex offender who is now dead.

“She caught my eye because she was dressed in purple plum clothes,” said Jenny Murat, who said she saw the woman standing on the street that night so many years ago, according to the Independent. “It struck me as strange.”

Murat said she alerted authorities once she heard about the situation.

“It’s so unusual for anyone, particularly a woman, to be standing alone on the street in our resort, just watching a building,” she said. “The next morning, we heard that a little girl had gone missing, and I later told police about the woman I’d seen right outside. I didn’t recognize her and don’t have a clue who she is, but she seems a bit suspicious.”

Authorities in London have spent around $13 million investigating Madeleine’s disappearance since she went missing 10 years ago. While Portuguese officials officially ended the investigation in 2008, Scotland Yard investigators opted to reopen it in 2013. Police were given an addition $260,000 in October to pursue a “person of significance,” according to the Sunday Times. Authorities said the lead was a “significant line of inquiry worth pursuing.”

Though minimal information has surfaced since she vanished, authorities said at the 10-year mark that it was still considered a missing persons case.

“There is every possibility that Madeleine is still alive and could be hidden somewhere,” said Dave Edgar, a former top detective who worked with the McCann family, according to News AU. “There’s countless isolated properties where Madeleine could be being held.”