London's Metropolitan Police, based at Scotland Yard, said authorities are combing phone records of tourist and residents who were at a Portuguese resort at the time 3-year-old Madeleine McCann disappeared, The Associated Press reported.
McCann vanished in 2007 while on a holiday vacation with her family in Praia da Luz, Portugal.
41 people of interest have been identified in the investigation, according to BBC News. Andy Redwood, the Detective Chief Inspector, who is leading the inquiry, said that officers have been examining a "substantial amount of data" from mobile phones. The phone records are from people staying at the resort.
"This is not just a general trawl. It's a targeted attack on that data to see if it assists us to find out what happened to Madeleine McCann at that time," Redwood said, explaining that police are trying to "identify the owner of each phone to build up a picture of exactly who was in the area," BBC News added.
Redwood admitted the difficulty of working with phones, which were bought six years ago on a pay-as-you-go basis, news reports said.
The police unit announced it was launching an investigation into McCann's disappearance in July after spending two years reviewing the case under its codename Operation Grange, BBC also reported.
Since July, British police formally requested cooperation with the Portuguese authorities. (Portuguese authorities previously dropped their investigation into her disappearance in 2008).
Detectives said that "fresh and substantive" information regarding the case will emerge on October 14, the date when BBC plans to broadcast a Crimewatch appeal. The show will feature a reconstruction and interviews with Madeleine's parents, Kate and Gerry, who, for the first time, will appear alongside detectives working on the investigation, BBC reported.
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