A guide to cell site analysis

What is cell site analysis?

Cell site analysis is a forensic method used by police intelligence analysts to identify where a mobile phone could have been at a particular time. The police intelligence analysts will use different sources of information to create a schedule. The information could include where the phone has moved to, who the phone was in contact with, the content of messages, ANPR information as well as CCTV images or vehicle tracking information.

Cell site analysis uses several different data points to pinpoint the location of a device at certain times. The techniques rely on data recorded by mobile network operators when a mobile phone interacts with the network in a recordable event. The mobile phone evidence can use mobile phone downloads (information extracted from the phone itself), connection records (i.e. from the network provider) and call data records which includes the ‘cells’ used to connect the calls and text messages. This includes passive records such as unanswered calls, received text messages and connecting to data through ongoing connections or automatic processes.

How does cell site analysis work?

The Police can request the Call Data Records (CDR) of a mobile phone under the Investigatory Powers Act. Once secured from the network provider, the records are analysed using specialist software. The mobile phone network infrastructure provided by service providers consist of a large amount of cell sites or masts which consist of numerous cells. The cells cover a limited geographical area, and each cell has a unique cell ID.

Analysis of CDRs is used by the Police to determine what cells were used by the mobile phone at or around a relevant time/date. They use this to conclude the location that a mobile phone was at during a certain time, although it could have been at other locations where the cell site has a usable signal.

The Police can assess if a Radio Frequency (RF) survey is needed. This is to see if the cells used at a certain time by the device provide coverage to a particular location which is linked to the investigation. RF surveys are done by the Police going to a place or driving a route and using specialised equipment to measure cells active in that area. The equipment is used to detect cells, which would then be able to assist in showing where a phone may or may not have been.

The Police then combine the call data records and RF surveys to produce a report.

What types of cases do the prosecution use cell site analysis in?

Cell site analysis is used in a variety of cases. However, it is most commonly used in serious matters involving multiple defendants. For example, cases including murder, drug conspiracies, county lines drug cases and people trafficking.

How reliable is cell site analysis?

An RF survey often doesn’t detect all available cells as it is done at street level and could be months after the phone was used in the alleged offence. Cells may be changed/decommissioned, and phones may be used in buildings on higher levels which could potentially expose them to different cells. It is impossible for any survey to be able to guarantee that the conditions under which the survey was conducted were the same at the time of any allegation occurring.

Although it is assumed that mobile phones would connect to the nearest cell site this is not always the case. There may be times when the nearest cell site is blocked in some way, for example by a building. In this case the mobile phone will connect to a cell site further away.

There is also overlap between neighbouring cells and the mobile phone may not connect to the nearest cell. The mobile phone may also connect to a different cell depending on whether it is connecting using 2G, 3G 4G or 5G.

Cell site analysis shouldn’t be used to geolocate a mobile phone or device to a specific property or exact location. Other evidence should be used to corroborate any conclusions about this.

At the moment there are network alterations taking place in order to implement 5G services and remove cells providing 3G services. This could also have an impact on the analysis and RF survey results.

Any changes to the landscape in a specific area can affect the coverage of cells. For example, new buildings or changes to the environment over time may reduce signal. The number of people using the cell with also impact the capacity of cells on the network.

Can cell site analysis identify who a phone belongs to?

Cell site analysis also cannot identify who the phone is attributed to. It cannot show who was holding the phone at what point. The police aim to use a common area of ‘residence’ and patterns of calls to attribute a phone to an individual. Cell site analysis can only say that a phone was in a certain area at a given time – this can range from one to tens of square kilometres in size. The analysis can give imprecise times a phone was used, especially if data from mobile/GPRS is being used.

Should a defence expert be instructed in cell site analysis cases?

If a defendant is contesting any findings in the prosecution’s cell site analysis, it may be worth instructing a defence expert to address any of the above issues. Given the variables discussed above with regards to the overlap between cell sites and the potential impact the environment including the size and nature of buildings may have on the accuracy of the analysis, it is often prudent to instruct a defence expert.

How can Olliers help?

At Olliers, our serious crime department has extensive experience of representing clients who face allegations which involve cell site analysis. We have positive working relationships with a number of defence -focused experts and will be on hand to guide clients through the often complex issues associated with cell site analysis and telephone attribution.

If you require advice in relation to serious criminal cases, please contact our new enquiry team either by email at info@olliers.com , or by telephone at 020 3883 6790 (London) or 0161 834 1515 (Manchester) or by completing the form below and our new enquiry team will contact you.