Your phone knows where you've been
Something that has come up a lot recently in trials is using mobile phones to place suspects at the scene of a crime. This is called cell siting, which uses the call data record from your phone company, and can provide important evidence for the defence or prosecution. To find out how your phone can tell tales, Georgia Mills spoke to Jason Coyne, an expert in digital forensics at IT-group...
Jason - Typically, when expert evidence is presented by the Crown, the defense team will generally call experts, such as ourselves, to look at any digital forensics and ask us to interpret that evidence for them. Often, it's a case of validating the evidence that's been provided but, also, quite often we find that mistakes have been made.
Georgia - Something that has become a lot more important recently in trials, is using mobile phones to place people at the scene of a crime. This is called CELL SITING, and it uses the call data record from your phone company. But, apparently, the picture is not always as clear as the prosecution would make it seem. So let's start - I'm getting a call from my friend, how does their voice reach me, and how does that notify the phone company to my location?
Jason - When your mobile phone is switch on and on the cellular network, it will negotiate which particular cell site or cell tower is best able to communicate your voice across the network to your friend. So, once it's connected to a particular cell site, the mobile network will actually register which cell site your mobile phone was on when a particular call event takes place. And they use that so they can a) root the call through to you successfully but also for the purposes for billing, and it's that cell site record that can be used to try and identify where you were geographically positioned at any point in time in history.
Georgia - So these towers, they're just dotted across the country?
Jason - They are. In the countryside, they look similar to big pylons with radio aerials on top but then, in the more urban areas, they're often positioned on businesses and you'll see a metal structure and then a series of aerials positioned around it. Typically, they have three aerials.
Georgia - How is this kind of information used by law enforcement?
Jason - What you will often find when you look through some of the papers that the police will provide as part of a court case, is you will see the instruction that they provided to the cell site analyst. What will often be the case is that the police are trying to put a suspect in a particular location. One that I'm looking at at the moment is where the suggestion is that a particular suspect was inside a shop at a particular point in the evening. And the instructions to the cell site analyst was to test whether the suspect was in the shop based on his call data record. So, what happens in that scenario, is the cell site analyst will go to that particular location in the shop, he will switch on his cell site measuring device, and he will see if he was connected to that particular cell site. If his device tells him that he would be connected to that cell site, then what often goes in the police report, is that the suspect was inside the building at that point in time.
Georgia - So, is it as simple as that? Put you at the scene of a crime - case solved!
Jason - It's not. It's not! Because the area that that cell site covers may well be 2/3/4, often 10 kilometers squared. So what you then need to do is after identifying that the suspect could well be in the shop, you've then really got to widen the circle and do what I call a 'range survey' to identify what other possible areas the suspect could have been.
Georgia - And this is something you've looked into for this case?
Jason - This is absolutely something that I've looked into for this case, and what we've found is that the suspect provided an alibi that he was actually at his girlfriend's house at the time that the robbery took place, and his girlfriend's house was about a kilometer away. But what I was able to do was I was able to cell site the retail shop and then go all the way from that shop to the girlfriend's house and, actually, at the girlfriend's house it was exactly the same cell site coverage. So, had he made a call from his girlfriend's house, the call data record would have been identical.
Georgia - I see. So at first glance this looked incriminating but, if you take a step back, it actually just supports his alibi?
Jason - Absolutely, yes. You've got to test both the positive case where you're trying to put the suspect, but really you've also got to consider what the possible range might be of that and look at the alibi cases as well, if you're going to test it properly.
Georgia - Do you think we'll see a trend in the future that this might get any more accurate?
Jason - Absolutely! I mean, with the early generation 2G mobile phones, the cell towers would typically cover 15 kilometers and it was very difficult to position anyone. With 3G, the cell sites come down to covering, typically, about 2 kilometers. The 4G cell sites that are built really for carrying a lot of data, we're finding less range still and, you'll find that in some high streets, there's quite a high saturation of 4G cell sites every few hundred meters. So, it could well be the case that if you have somebody that's conducting a telephone call and that telephone call is handled by three or four different cell sites, then you can probably position that suspect with some degree of precision as they walk down that street.
Georgia - This kind of technology is leaving a big stamp on the justice system. The Hatton Garden raid has been noted as the BIGGEST robbery in British History after a group of men nicked about 14million pounds worth of jewellery. The gang even studied forensics in a bid to avoid leaving a trail but forgot about this new technology, they'd all had their phones on them. And cell siting isn't the only way your phone might tell tales on you...
Jason - A lot of work that we do now is actually on looking at the methods of communication between suspects because we find that often now, when crime is committed, people will take photographs and those photographs have a geolocation. So they are able to locate where the individual was when the photograph was taken and then, as these are exchanged through social media and things like that, there's quite a trail that can be examined.
Georgia - Wow! That sounds incredibly stupid to take a photo like a selfie in front of a robbery?
Jason - Yes, absolutely. We certainly see that. We often see that with crimes where people have stolen currency. So people, it would seem, like to have their photograph taken with large wads of cash in their hands.
Georgia - Jason Coyne, from ITgroup there.