Mobile phones can provide an important source of evidence in criminal investigations. Police may obtain records showing when a particular phone was being used, the communications made from it and which part of the mobile network handled those communications. In some cases, this information can help establish the general area in which a phone was being used at a particular time.
This is known as cell site analysis. It can be relevant in many different types of criminal case, particularly where the prosecution seeks to establish a person’s movements or suggest that their phone was in the area of an alleged offence. However, cell site evidence is often misunderstood. It is not the same as GPS tracking, it does not necessarily show the exact location of a phone and it does not automatically prove that the defendant was the person carrying the phone.
Understanding those distinctions is important when assessing both the strength and the limitations of mobile phone evidence.
What is cell site analysis?
Mobile phone networks are divided into areas of coverage called cells. These are served by physical cell sites, commonly referred to as mobile phone masts. A single site can serve more than one area because it may have different antennas or sectors pointing in different directions.
When a phone communicates with the mobile network, the network can record information about that activity. Depending on the type of communication and the records available, this can include the date and time, the phone number or other identifying information and the particular cell or sector through which the communication was handled.
Cell site analysis involves examining those records to consider where the phone was likely to have been operating. The current Forensic Science Regulator’s statutory Code of Practice specifically covers cell site analysis for geolocation as a recognised forensic activity. More detailed examinations can involve analysing the network records, mapping the relevant cells and carrying out technical surveys to understand the coverage provided by them.
Not every piece of mobile phone analysis is necessarily a full forensic cell site examination. Police may also use communications data simply to investigate a case or establish a chronology. The current forensic framework distinguishes this investigative analysis from a formal cell site analysis undertaken to provide a geographical opinion for evidential purposes.
Does a phone always connect to the nearest mast?
No. This is one of the most common misconceptions about cell site evidence.
A mobile phone does not simply connect to whichever mast happens to be physically closest. The connection can be affected by the strength of the signal, the way the network has been designed, buildings, hills and other geographical features, as well as the amount of traffic being handled by the network. A phone can therefo re connect to a cell which is not the nearest physical site.
This does not mean that cell site evidence is unreliable. It means that the evidence has to be understood properly. The fact that a phone connected to a particular cell can be useful evidence, but what that connection tells us about the phone’s location depends upon the particular network and the technical evidence available.
What information can the police obtain?
Cell site analysis commonly involves communications data, including information often referred to as Call Data Records or CDRs. These are records held by communications providers which can contain information about communications and the network connections involved.
The precise information available depends upon the provider, the type of communication and the relevant period. Records can include information relating to telephone calls, text messages and certain forms of data activity, together with the relevant times and network information.
The acquisition of communications data is governed primarily by Part 3 of the Investigatory Powers Act 2016, together with the applicable Communications Data Code of Practice. The legislation and Code provide an important framework for the lawful acquisition and disclosure of communications data and set out safeguards governing its acquisition. Other forms of lawful authority may also apply in particular circumstances.
It is important to distinguish network records from information taken directly from a phone. If police seize a handset, it may contain messages, photographs, application data, location information and other material which is not contained in the network provider’s records. Communications made through applications or over Wi-Fi can also produce different types of evidence. The CPS recognises that the information available from a provider may differ where communications are made through applications such as WhatsApp or where Wi-Fi is being used.
What can cell site analysis actually show?
At its most basic level, cell site analysis can help establish the general area in which a phone was operating at a particular time. A sequence of records can sometimes also help investigators examine whether a phone appears to have moved between different areas. In appropriate cases, the records from two phones can be compared when considering whether their movements may have been connected.
The amount of information that can be obtained from the records will vary considerably from case to case. The CPS explains that cell site analysis can determine the general location of a SIM-enabled device, but that it may not identify a specific location such as a particular address or street. The current Forensic Science Regulator Code likewise recognises the uncertainty involved and makes clear that cell site analysis cannot pinpoint the precise location of the device.
This distinction is important. Evidence that a phone used a cell which served an area containing the location of an alleged offence is not automatically evidence that the phone was at the precise location of that offence. There is an even further step between showing where a phone was operating and proving that the defendant was physically there.
Similarly, a series of cells used by a phone may support an inference that the phone travelled between areas, but it will not necessarily establish the precise route taken or every location at which the phone stopped. The conclusion must reflect what the underlying evidence can properly support.
Does cell site evidence prove who had the phone?
No. This is another important distinction.
Cell site analysis is evidence about the phone or SIM and its activity on the network. It does not, by itself, establish who was carrying or using the phone at a particular moment.
A phone may be registered to one person but used by somebody else. It may also have been lent, shared or transferred. The name attached to a mobile account can therefore be relevant, but it does not necessarily answer the question of who had the phone when the alleged offence took place.
Other evidence may help with that question. This could include messages, photographs, information recovered from the handset, CCTV, ANPR, financial records, witness evidence or evidence concerning the defendant’s usual use of the phone.
The current Forensic Science Regulator Code recognises this issue as attribution: the process of considering whether a particular device can properly be associated with an individual. Cell site evidence may contribute to that assessment, but it is not itself a guarantee of identity.
Can cell site analysis show that someone was at an exact address?
Usually, cell site analysis alone cannot establish that a person was standing at a particular address.
A cell can cover an area containing numerous streets and buildings. The fact that a phone used that cell therefore does not mean that the phone must have been at any one particular property within the coverage area.
The CPS specifically explains that cell site analysis may establish a general location without identifying a specific address or street. The Forensic Science Regulator Code also recognises that the technique cannot pinpoint the precise location of the device. The level of geographical detail that can properly be expressed will depend upon the particular network, the relevant cells, the available records and any technical survey work.
The wording used by an analyst or expert is therefore important. Expressions such as “in the vicinity of” and “consistent with” can sound more precise than they really are if they are not properly explained. The current Forensic Science Regulator Code contains specific requirements concerning the use of these expressions so that reports do not give the court a misleading impression of certainty.
Can the defence challenge cell site evidence?
Yes. Where cell site evidence is important to the prosecution case, it may be necessary to look beyond the headline conclusion and examine how that conclusion was reached.
The appropriate questions will depend upon the case. They may include whether the underlying records are complete, which cells and sectors were involved, how the data was processed, what the network looked like at the relevant time, whether a survey was undertaken and what assumptions were made when interpreting the results. The issue of who actually had the phone may also be important if the prosecution relies upon the phone’s location as evidence of the defendant’s own location.
Disclosure can form part of that process. The CPS Disclosure Manual recognises the use of communications data and analytical tools, including geographical mapping of cell site information, and explains how digital material should be considered within the disclosure process. It also recognises circumstances in which defence analysts or experts may require communications data relevant to an issue in the case. This does not mean that the defence is automatically entitled to every record held by a telecommunications provider; disclosure remains governed by the applicable legal principles.
Challenging cell site evidence is therefore not simply about finding a technical imperfection. It is about ensuring that the conclusion being relied upon by the prosecution is properly supported and that the court understands the limits of what the evidence can establish.
Cell site evidence and the rest of the case
Cell site evidence is commonly considered alongside other evidence rather than in isolation. Police may compare it with CCTV, ANPR, witness accounts, messages, information recovered from a handset, financial records, vehicle evidence and other material when constructing a chronology of events.
For example, cell site evidence may indicate that a phone was operating within a particular area, while CCTV may address whether the defendant was physically present there. Handset evidence may help establish who was using the phone, while messages or financial records may provide entirely separate evidence about what the defendant was doing.
The same principle applies when considering a defence case. A cell site record may appear to support one part of the prosecution’s account, but its significance has to be assessed alongside the rest of the evidence. Equally, evidence suggesting that the defendant was elsewhere may be important when considering the weight that should be placed upon the location of the phone.
Cell site analysis can therefore be a valuable form of evidence, but its proper significance depends upon what it actually establishes and how it fits with the evidence as a whole.
A practical example
Imagine that a defendant is alleged to have travelled to a particular town and committed an offence at about 9pm. The prosecution relies upon records showing that a phone associated with the defendant communicated with a cell serving part of that town at around the relevant time.
The records may provide evidence that the phone was using that part of the mobile network. Further technical analysis might help establish the areas in which the relevant cell could provide coverage. That could make the evidence relevant to the question of where the phone may have been.
It would not automatically prove that the phone was at the exact location of the offence, nor would it by itself prove that the defendant was carrying the phone at 9pm. Those are separate questions which would need to be considered against the technical evidence and the rest of the prosecution case.
If, for example, CCTV showed the defendant elsewhere or there was evidence that another person had access to the phone, that could affect the significance of the cell site evidence. The court would ultimately have to assess all of the evidence rather than treating the use of a particular cell as conclusive proof of the defendant’s location.
Frequently Asked Questions
Is cell site analysis the same as GPS?
No. GPS and cell site analysis are different types of location evidence. Cell site analysis considers the mobile network connection used by a device and generally provides information about the area in which the device may have been operating rather than precise GPS coordinates.
Does a phone always connect to the nearest mast?
No. A phone can connect to a cell which is not the nearest physical site. Signal strength, network configuration, buildings, terrain and other factors can affect which cell serves the device.
Can cell site evidence prove that I was at a particular address?
Not by itself. The relevant cell may cover a wider area, and the precise conclusion depends upon the particular network and any technical analysis undertaken.
Does cell site analysis prove who was using the phone?
No. It provides evidence about the device or SIM and its network activity. Establishing who was carrying or using it is a separate question.
Can two phones using the same cell prove that two people were together?
No. Two devices using the same cell does not, by itself, establish that their users were together. The timing, coverage and other evidence would need to be considered.
Can the defence challenge cell site evidence?
Yes. Depending upon the circumstances, it may be possible to examine the underlying records, network configuration, survey work, methodology, attribution and the way the conclusions have been expressed.
Does mobile phone evidence always come from the network provider?
No. Network records are one source of evidence. A seized handset may contain messages, photographs, application data and other information which can provide different evidence about the phone and its user.
How Empire Law Can Help
Where cell site evidence forms part of a prosecution case, it is important to understand exactly what the evidence shows and what conclusions can properly be drawn from it. The distinction between the location of a phone, the location of the person carrying it and the identity of the person using it can be particularly important where mobile phone evidence is relied upon to place a defendant at or near the scene of an alleged offence.
Empire Law can advise defendants where cell site analysis or other mobile phone evidence forms part of the prosecution case. Depending upon the circumstances, this may involve considering the underlying evidence, disclosure, the question of attribution and whether specialist technical advice is required.
