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Madeleine McCann: What data could investigators gather from suspect's mobile phone number?

James Titcomb
Nokia phone - Asim Hafeez/Bloomberg

Modern smartphones contain a trove of personal data linked to social media accounts, internet storage services and satellite navigation apps, which have made them a vital resource for criminal investigations.

But in 2007, when Madeleine McCann went missing from the Portuguese resort of Praia da Luz, the iPhone was still a month away from going on sale. Most people carried basic mobile phones without touchscreens, internet connections and GPS chips.

However, mobile phone records, including location data and records of calls and texts made between numbers, could still be used to trace criminal suspects and potential accomplices.

On Wednesday, Scotland Yard said a 30-minute phone call was made to a Portuguese phone owned by a newly-identified suspect in its investigation into Madeleine’s disappearance, just an hour before she vanished.

The key to obtaining mobile phone data in the days before internet-equipped phones was through the mobile operator a phone number was registered to. Since most phones did not have Wi-Fi connections, all calls and text messages would have had to travel over a mobile network.

Portugal’s three mobile networks - TMN, Vodafone and Optimus - would hold a record of every phone call and text message made and received by a number for billing purposes, including how long phone calls lasted for, and what number was on the other end of the line.

Madeleine McCann - AP

Networks would also have been able to roughly track users’ locations, by seeing which cellular base station a phone had “pinged” at any one moment. Mobile phones are constantly communicating with these towers when they are turned on, and finding the rough location of a phone is simply a case of seeing which station it communicated with.

Advanced techniques allowed police to more accurately gauge a phone’s location by triangulating its signal between multiple cell towers, although this is easier in urban areas with many towers than in coastal Portugal, where coverage may have been patchy in 2007.

Location data based on cell towers is also not as accurate as GPS, and has previously been thrown out of court for being unreliable.

Retrieving what was said in text messages and phone calls is more difficult, however. Without a wiretap arranged in advance through a court order, networks do not tend to keep the content of messages or recordings of phone calls, although voicemails were typically stored by network operators.

What was often more difficult was connecting a phone number to an individual. While mobile phones with monthly contracts were linked to billing information and addresses, pay as you go phones, in which credit could be purchased up front in cash, did not have to be registered.

This allowed for “burner” phones that could be used for criminal activity and be disposed of. Portugal introduced the world’s first pay as you go phone, and it was easy for foreign visitors, such as the German national identified in the Madeleine McCann investigation, to buy top-up SIM cards without ID checks.

Police said they were attempting to discover who called the suspect in an attempt to learn more about his movementrs.

Investigating a case that is over a decade old also means that mobile phone data may be long-gone: networks typically store data for between one and five years before it is deleted. That suggests investigators may have had this data for several years, or that deletion of the records was put on hold.