A missing poster for Madeleine McCann appears on a website dedicated to finding her. McCann Family

Almost 10 years after 3-year-old Madeleine McCann disappeared during a family vacation in Portugal, police announced they were still hard at work investigation the abduction. British investigators said Tuesday four detectives continued to look into critical leads in the case.

“I know we have a significant line of inquiry which is worth pursuing,” London’s Metropolitan Police Assistant Commissioner Mark Rowley said, according to the Press Association. “And because it’s worth pursuing, it could provide an answer. But until we’ve gone through it, I won’t know whether we are going to get there or not.”

Madeleine vanished May 3, 2007, after her parents left her alone in an unlocked rented vacation apartment in Portugal along with her 2-year-old twin siblings. They went out to dinner. Portuguese authorities ended their investigation in 2008, while Scotland Yard investigators opted to reopen the case in 2013.

A missing poster for Madeleine appears on a website dedicated to finding her. McCann Family

“We’ve got some critical lines of inquiry, those link to particular hypotheses,” said Rowley. “But I’m not going to discuss those because those are very much live investigation.”

Madeleine’s parents, Gerry and Kate, were cleared in relation to their daughter’s disappearance, as were four people who were declared suspects in 2013.

“Ten years — there’s no easy way to say it, describe it, accept it,” Madeleine’s parents wrote in an update on the website dedicated to finding her Monday. “I remember when Madeleine first disappeared, I couldn’t even begin to consider anything in terms of years. And now here we are… Madeleine, our Madeleine — 10 years.”

There was no evidence pointing to whether Madeleine was alive or dead at this point, Rowley said in a statement released ahead of the ten year anniversary of her disappearance.

“It is a missing person’s inquiry,” he said. “But as a team we are realistic about what we might be dealing with—especially as months turn to years.”

An age progression shows what Madeleine McCann would look like at 9 years old. McCann Family