LONDON - British police said Friday that analysis of mobile phone data from thousands of people who were in a Portuguese resort when British girl Madeleine McCann disappeared in 2007 could provide a new lead.
A major appeal based on "substantive" new information will be broadcast on a BBC television programme on October 14.
Police are analysing data from phones belonging to people who were in Praia da Luz when Madeleine vanished in May 2007 and they are investigating 41 potential suspects, although no arrests have been made.
"The mobile phone data is a substantial amount of data," said Detective Chief Inspector Andy Redwood, who is leading the inquiry, but he added that much of it was "unattributable".
"Putting this with layers and layers of other information, we are carrying out a targeted attack on the information. It is like pulling back the layers of an onion," he said.
Redwood admitted officers had so far been unable to match a "large number" of mobile numbers to the users of the phones. He said the task was complicated by the fact that many of the phones operated on a pay-as-you-go basis.
Madeleine's parents Gerry and Kate McCann have never abandoned their campaign to find Madeleine, who was just about to turn four when she disappeared as she slept in the family's holiday apartment on May 3, 2007. Her parents were dining with friends in a nearby restaurant at the time.
Portuguese authorities closed their investigation in 2008. But London's Metropolitan Police spent two years reviewing the evidence and announced in July that they were launching an investigation into Madeleine's disappearance.
British police are working with senior detectives from Faro, in the Algarve.
Redwood said the phone records contain information about which phone numbers were dialled and when calls were made.
"We can see what the phone is doing, but we can't see the text messages," said the detective. "It shows a timeline of the call data."
Scotland Yard said the phone records were "looked at" during the initial Portuguese police investigation, but not in detail.
Asked by reporters if the information could provide a breakthrough in the investigation, Redwood said: "It could do."
The investigation is however being hampered by the lack of CCTV footage.
In July, detectives said there were 38 "persons of interest" from five different countries - Portugal, Britain and three others that were not named.
Police said the number had now gone up to 41, of whom 15 were British nationals, but no arrests have been made.
Madeleine's parents say they refuse to believe she is dead.