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Over the past decade, we have built the largest pool of private sector cell site expertise anywhere in Europe. Our team members are award-winning; published regularly in scientific journals; called as expert witnesses for both prosecution and defence; and consult regularly with the Forensic Science Regulator on standards and best practice.
For some forces, we are their cell site analysis team; for others, we bring extra resource or particular skillsets; and for all forces and for defence counsel, we are able to go further than analysts’ presentation of factual call data with expert opinion.
As the science matures, there’s also continued innovation. We don't just analyse, our Cell Site Scene Preservation service gives LEAs a reliable, affordable way to overcome the challenges brought on by UK mobile network operators and their rapid reconfiguration of their mobile networks.
Preserving the cell scene early mitigates the risk of the mobile network changing between the time any calls were made by a target phone and the eventual survey – which in turn can seriously undermine the validity of any Cell Site evidence presented in court.
If you are interested in our Cell Site Preservation service, please download our brochures here:
To get up to date with the latest on legal obligations and standards around cell site analysis, download our white paper here.
Case studies - the real life application of cell site analysis
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Get in touchData stored on mobile phones is a common source of investigative and evidential material, but there may be further useful information available such as Call Data Records (CDRs), held by network operators for billing purposes. This information is potentially available to be used within criminal investigations.
Historic Cell Site Analysis involves the analysis of these records, in conjunction with other information such as survey and geographic data, to determine areas where a mobile device may have been at the time of call activity recorded by the network. This is also referred to as ‘Geo Location’ with the FSR code. The analysis may enable investigative insights as to the area in which the device was (and it is always an area) or potential movement. If used at court, an evaluative assessment of whether the data might (or might not) be expected given the positions taken by the Prosecution and/or Defence can also be made.
The concepts of Cell Site Analysis are relatively simple:
• When a mobile device interacts with a telecommunication network, a record of that interaction may be retained which can include the Cell Site (mast location) and the specific Cell (unique to a specific aerial) used.
• These records may be available, with appropriate legal authority, to organisations within Law Enforcement and the wider Criminal Justice System.
• Inference can be made as to the area in which a device was at the time of the activity, and this assessment may be used to better inform an investigation or aid the jury in coming to their view on the guilt or otherwise of the accused.
A common misconception is that Cell Site Analysis can pinpoint a device to a specific location. Cell Site Analysis can provide an insight to the area in which the device was.
However, probably the most dangerous misconception is that Cell Site Analysis is a simple, factual process and that it is safe to just present maps and tables from the Call Data to a jury for them to make their minds up on what it all means. There is uncertainty throughout the process; this includes initial generation of the Call Data on which the analysis relies (which is designed for billing, not forensic purposes) and through each subsequent process within the analysis (survey measurements in particular). This means that the execution of Cell Site Analysis can be anything but simple, and it always results in opinion.
Unfortunately, unsafe practice is widespread in the field, for example presenting “factual” maps and tables to the jury. Relying on 2D maps to draw safe inferences from the data is only safe in the broadest of questions (e.g. movement between cities) – and even then can be problematic if it relies on GPRS data, which cannot safely be taken at face value. It isn’t just “facts and common sense”, there can be nuance. These issues concerning reliability within telecommunication evidence came to a head in R v Calland, in which there was a ruling by the Court of Appeal. One of the concerns raised by the Defence was that [the prosecution had] “…unhelpfully conflated the location of a particular mast with the question of what safe inferences can be drawn about the telephone using it”; this objection was upheld.
The FSR Statutory Code recognises the risk that poor practice in Cell Site Analysis presents to the Criminal Justice System and defines acceptable (and unacceptable) approaches. CCL comply with the statutory FSR Code.
Well, if you’re interested in recovering deleted information, we have a world-class team of mobile phone experts who specialise in just that – so yes, this might be possible. From a Cell Site Analysis perspective, however, the networks don’t keep content (e.g. a message) so it makes no difference if it’s deleted on the phone or not, we won’t see it either way.
Cell Site Analysis isn’t concerned with content, however, it’s concerned with Call Data surrounding the content that is held by the network. The phone doesn’t even need to have been recovered for an analysis to take place, and a user can’t delete their Call Data Records even if they wanted to. Every UK network stores Call Data Records for up to 12 months, so as long as the request is within this period, Cell Site Analysis may be possible.
There are 2 main ways in which Cell Site Analysis can provide insight at court:
1. The activity of a phone in a given period – for example whether the Call Data might be expected if it were at the scene or alibi locations.
2. Aiding in an attribution assessment. If there is an alleged (“dirty”) phone, we can compare that data with that which we might expect if it was used by the suspect. This can be done by comparing the “dirty” phone data against known movements (via attributed, or “clean” phone data, ANPR, observations etc.) and areas of common usage (compared to known home and work addresses, for example).
Cell Site Analysis is particularly useful in cases where understanding someone's movements is crucial, such as in criminal investigations or family law cases.
A given phone number is associated with the SIM card, not the handset, but there is also a unique identifier for the handset – the IMEI (the International Mobile Equipment Identifier). This is often recorded in CDRs and, if the same IMEI occurs in the CDRs for more than one phone, it is a relatively trivial matter to detect this. This can be very useful as part of a wider attribution assessment, which can include other non-cell site factors such as numbers with which different phones (for example the attributed contract phone and the alleged phone) have been in contact in common with each other.
• First of all, we never know where the phone was, but we may know the Cell ID to which it was connected at a given time. Cells serve areas, and we’ll never get away from that. No matter how well we are able to develop technical methods, we will never be able to pinpoint the exact location of the phone.
• The Call Data Records we consider weren’t designed to help us work out where someone was, they were intended for billing purposes. This means that if we take them at face value they can misleading; this is particularly pertinent to analysis of “data” events (otherwise known as “GPRS”) in which, amongst other issues, the indicated time of a connection to a given cell may not be true.
• Estimating the area over which a cell serves can also pose a challenge, there’s a lot more to it than plotting where the mast is. The areas cells serve can change with time and this is another uncertainty we must accommodate in our analysis. All is not lost, however. We are often able to make an assessment of changes, and indeed have published research on this problem.
Additional information concerning the cell used in a given call event may be detailed in the Call Data records. This detail can include the cell site location, azimuth etc. which can be used as a preliminary estimate of the anticipated service area (i.e., the cell is expected to serve from the mast location and into a wider area in the approximate direction of the azimuth). The estimate can be refined by considering survey data, terrain profiles, expected or known presence/absence of other Cell Sites etc.
Survey data can be very useful when doing this, but it is not perfect. At CCL we have state of the art equipment, and our validated survey methods include the ability to monitor every network and technology simultaneously. We store this data into a database, currently running at approximately 800 million measurements, that can help us estimate the total service area of a cell and also whether there may have been changes to the network between the times of the calls in the CDR and the times of any targeted surveys tasked to aid in the specific case we are working on. This can be very powerful when informing opinion as we have a breadth and depth of ground-truth data built up over many years.
Within section 110 (“Cell site analysis for geolocation”) of the Statutory FSR Code, it states:
“110.9.10 The location of the device is not in the CDRs, but the area in which it was operating may be inferred from the detail within the records. Inference is synonymous with opinion, and therefore should be given by a practitioner who is competent to provide evidence of opinion (i.e. an expert). If the purpose of the analysis is to assess where the phone was, this will require the practitioner reporting the finding to be giving an expert opinion.
110.9.11 Expressing opinions is the role of the expert witness; this includes providing evaluative evidence. Practitioners interpreting results shall have been assessed and deemed competent in interpretation and opinions”.
All reports containing opinion from CCL are issued by a competent expert who complies with the rules, regulations and standards concerning expert evidence for England and Wales.
The quotes above from the Code mention “Evaluative” evidence. This is when the probability of the evidence (i.e. the CDRs) given the position taken by prosecution is compared to that of the defence. This is in contrast to ”investigative” opinion, which provides speculative explanations for the data. Confusing the two can cause serious issues in opinion evidence at court and can result in “the prosecutor’s fallacy” (or “Transposed Conditional”) which can be grounds for appeal. This is another reason why just presenting “factual” prosecution-selected maps and tables to explain why the suspect did it is an unsound approach to evidential Cell Site Analysis.
The FSR statutory Code defines Best Practice; it is the de-facto standard for Cell Site Analysis in England and Wales. There is no obligation to comply with it until October 2025, but if practitioners don’t comply, their work will -by definition- be substandard. Criminal Practice Directions (related to Criminal Procedure Rules) that includes use of expert evidence; CrimPD applies now. At the core of the Codes is the requirement for a practitioner to be able to demonstrate the validity of the methods they use and their own competence. This means that some current practice is no longer permissible:
• The production of maps and tables and presentation to juries without overt opinion on the meaning of them in the context of a case.
• Impressive CVs with reports essentially saying “I’ve been doing this ages, it matches because I say it matches” without auditable documentation of validation, competency, processes, information security etc.
CCL’s Standard Operating Procedures are based on, and comply with, Good Industry Practice as defined in:
• CrimPR/ CrimPD
• The statutory FSR Code, in particular DIG-200 (Geo-location)
• FSR-C-118 (Interpretation)
• FSR-G-217 (Cognitive Bias)
• The AFSP standard for Opinion Evidence
• Royal Statistical Society (RSS) guidance
Formulation of Opinion by CCL experts follows the Case Assessment and Interpretation Model as extensively used in “traditional” forensic science (such as DNA, glass, fibres etc.). The processes adopted by CCL are those considered “Best Practice” by the European Network of Forensic Science Institutes (ENFSI), whose membership contains governmental laboratories in 39 countries.
It’s fair to say that the introduction of the FSR Code will present a challenge to the way that many organisations (LEAs, Companies and lone practitioners) operate. A discussion of the statutory FSR Code and its effect on current practice (mainly “factual” analyst product presented straight to the jury) can be found here. (LINK TO WHITE PAPER the one sent to Sarah).
Technology changes, understanding of artefacts changes, approaches to inference can be affected by ruling in other areas of forensic science. Experts must stay on top of developments, so R&D is critical. CCL have an active research program addressing every aspect of Cell Site Analysis, including assessing uncertainties in the Call Data, development of novel methods to analyse it, and how to formulate sound opinion. Some elements of our research have been published in the academically peer-reviewed Q1 scientific journals (“Science & Justice” and “Digital Investigation”):
• “Historic Cell Site Analysis – Overview of Principles and Survey Methodologies”, https://doi.org/10.1016/j.diin.2011.10.002
• “Cell site analysis: Roles and interpretation”, https://doi.org/10.1016/j.scijus.2019.06.005
• “Opinion evidence in Cell Site Analysis”, Awarded a PW Allen commendation from the Chartered Society of Forensic Sciences as one of the “most meritorious” in any field of forensic science that year based on a range of factors, including the quality of the science. https://doi.org/10.1016/j.scijus.2020.02.002
• “Cell site analysis; Use and Reliability of Survey Methods”, https://doi.org/10.1016/j.fsidi.2021.301222
• “Cell site analysis: Changes to networks with time”, https://doi.org/10.1016/j.scijus.2022.04.001
• Elsevier Major Reference Work (MRW) - “Encyclopedia of Forensic Science (3rd Edition) ISBN 978-0-12-823678-9. Chapter: “Forensic Inference from telecommunication Records”
Collectively, these papers form much of the academically peer-reviewed foundation for the field. If the papers are too dry, why don’t you just call? The problem won’t be getting an expert to talk with you, it’ll be getting them to shut up… (it’s a very interesting field).