British police on Friday said they would conduct a "targeted attack" on mobile phone data of people who were near the Portuguese resort of Praia da Luz when British girl Madeleine McCann disappeared in 2007.
Detective chief inspector Andy Redwood said the phone data was now being cross-referenced with other information.
"The mobile phone data is a substantial amount of data and a significant amount of it is unattributed," he explained.
"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."
Madeleine's parents Gerry and Kate McCann have never abandoned their high-profile campaign to find their eldest daughter who disappeared on holiday on the Portuguese south coast on May 3, 2007, shortly before her fourth birthday.
Portuguese authorities have refused appeals to reopen their investigation, but six detectives are in Portugal working on behalf of Britain's Metropolitan police.