Analysis of over 100 mobile phones played a key role in the investigation of last year's £50m Securitas depot raid in Tonbridge, vnunet.com can reveal.

Specialist mobile phone investigation business Forensic Telecommunications Services, was called into to extract evidence from these phones.

Hans Taylor, business development manager, of FTS explained that the number of phones analysed for evidence in crimes spread out ‘like ripples in a pond’.

“A lot of times the examination is to eliminate a person from an inquiry.”

But criminals do like their phones, he added. “Typically a professional criminal will have two to three mobile phones on them, and up to 10 SIMs. They swap the SIM every time they make a call,” said Taylor.

“A simple robbery involves two to five mobile phones. For a small drug deal, there’s easily five to 10 mobile phones. These figures are based on how many phones we’re given associated with the different kinds of crime we’re asked to investigate.

“Illegal immigration rings tend to be quite closed shop, however there can be at least 20 mobile phones need examining. Contract killings don’t happen often, but typically 50 plus mobile phones might need to be examined as the result of a single person being murdered as the result of an organised crime.

The big numbers really add up in terrorism investigations like the one for the plot to detonate bombs on the London transport system on 21 July 2005. “That resulted in 300 mobile phones being examined and there were only four people,” says Taylor.

Taylor was speaking at the International Crime Science Conference 2007 in London. “It’s almost impossible to get no evidence from a mobile phone,” he says.

“Even if there’s no useful digital evidence it could have physical evidence on it – you hold it, you touch it, you talk into it. There’s a lot of evidence on mobile phones.”

He describes the basic information police can get from a mobile phone as baseline evidence. This is the missed calls, dialled calls, calls received, text messages, dates and times, serial number, and make up 80 per cent to 90 per cent of all forensic mobile phone analysis.

“You don’t tend to have much smoking gun evidence, but occasionally text messages will have content which proves something straight away,” says Taylor. “Pictures and video clips that’s where you tend to find smoking gun evidence.

“Most part it’s about attribution, association, identification. But just because the phone has been doing all these things doesn’t mean the person has.”

A real issue with getting baseline evidence is that when you take a SIM, which wasn’t the last SIM that phone used to make a connection to network, or even when powered on, the phone will wipe half the base-line data. The experts can’t risk putting a SIM back in the phone.

The information FTS specialises in getting is from the phones memory chip, not SIM or memory cards. The conditions for doing a straightforward logical examination of the phone are that FTS can get into the phone, they can turn it on, it works and it’s not pin-locked.

But then, just because you can turn it the phone on doesn’t mean you can get at deleted data. “It’s not like computer forensics,” says Taylor.

FTS’ real skill is getting the deleted data, and getting deleted data from the memory chip of damaged phones. “We see burnt phones, water damaged ones – surprisingly people think because its electrical water will create damage.

“Physical damage is becoming very common, and lots of people have flip phones. The first thing a criminal will do is snap it.”

Taylor gives the example of Motorola’s V3 which is very popular and also easy to damage. But FTS adds 10 to 30 new phone models a month to its forensic capabilities.

He says the work of FTS solicits quite a lot of guilty pleas. “We can get that deleted information criminals don’t want you to get. That’s the cheapest kind of prosecution there is.”