Investigators in the disappearance of Madeleine McCann have travelled to Bulgaria to pursue a new lead, it has been revealed.
Following a credible new tip, detectives are seeking a mysterious figure known as "the woman in purple", who may be the key to the decade-long mystery.
The Sun newspaper has revealed the woman's now-dead husband was a convicted paedophile.
The two were working as domestic helpers near the Algarve apartment in Portugal where Madeleine disappeared in 2007. They were reported to police by locals soon after the three-year-old's disappearance, but these reports were not followed up until Scotland Yard officers recently re-examined statements.
Witnesses say they saw the woman near the Ocean Club complex in Praia da Luz, where the McCann family was staying. Neither she nor her husband was seen again after Madeleine went missing.
Police were unable to locate "the woman in purple" despite extensive searches, but a recent breakthrough has taken authorities to Bulgaria, Eastern Europe.
The news comes after last month's revelation police had identified a key "person of significance" in the McCann case. The Times reported a source close to Scotland Yard's investigation said the person is now a "critical line of inquiry".
Madeleine disappeared from the holiday apartment her family was staying at on the evening of May 3, 2007. She and her younger twin siblings were left unsupervised while their parents were out having dinner.
She was discovered to be missing at around 10pm, and has not been seen since. It remains one of the most high-profile missing person cases in modern history.