The monthly cell site blog is back – and this month, we’ll be looking at what makes for an high impact piece of cell site evidence in court, as well as how going that extra mile at the outset of a cell site investigation can, in the long run, save time, money and bring your case to a speedier, more positive conclusion.
Impactive court presentation
By Dr. Iain Brodie, Cell Site Expert
Let’s consider a real case which CCL-Forensics investigated on behalf of a UK police force. We’ll change some of the location and crime details for the sake of confidentiality, and to help with legalities. The story goes like this: there was an aggravated burglary at a house in a semi-rural location, and following enquiries, a man was arrested. It was crucial for the prosecution to demonstrate the man was at the scene and not merely in the vicinity.
The prosecution claimed that the man in custody had made a number of phone calls to an accomplice, waiting outside the property, while the crime was in progress. They obtained the call data records (CDRs) from the phone company which the phone (attributed to the individual) was connected to at the time.
CCL-Forensics cell site experts looked at the calls at the pertinent time, and could see that there were indeed incoming and outgoing calls – as well as a number of texts. These events on the CDR used three different cell IDs (mobile phone mast sectors), but all took place over the period of a number of minutes.
In order to determine whether the suspect was likely to have been at the scene, surveys were carried out of the entire coverage areas of these three cells. CCL-Forensics performed a number of drive surveys, looking at areas where the cells in question would initiate a mobile phone call. Once these drive surveys had been carried out, for each of the three masts, they were uploaded onto our mapping system and the so-called ‘derived service areas’ were plotted.
The result was instantly compelling. Like a neat Venn diagram, the areas overlapped, with that overlap area covering a comparatively small area. Well within this area, was the crime scene. It was, to a certain extent, a ‘textbook’ piece of evidence. The fact that a number of cells were used at the time could easily be down to the fact that the suspect was moving around the house, and receiving a different dominant signal from different elevations of the property.
The question you may well ask, is why not just carry out a ‘spot sample’ at the crime location? Surely this would have yielded the same result. The reason for this was down to the case conference CCL-Forensics held with the investigating officer, where it was felt that a more robust survey was required to pre-empt any possible challenge from the defence. This turned out to be a very wise move, as in the weeks after the survey was carried out, the defence put forward an alibi location which was only a comparatively short distance from the crime scene.
When this point was plotted on the same map (without the need to go out and re-survey), it does indeed show that one of the cells served (for initiating a call) at this location – but not all three. The alibi location was therefore rejected, and based on the compelling evidence from cell site analysis, the suspect was found guilty.
The map shows the coverage areas, along with the overlap, which ultimately proved to be the pivotal piece of evidence in court. When presented to the jury in this way, the impact is immeasurable.
The remit here was to find an effective balance between doing the bare minimum, and doing too much – incurring unnecessary costs. Had a simple ‘spot sample’ been carried out in the first instance, it would have been necessary to return to the scene to carry out similar exercises at the alibi location – incurring delay and cost. As it transpired, this was not necessary, as the measurements had already been taken. In addition to this, the way the evidence was presented, showing the relevance of the small area where the cells’ service overlapped, proved to be an invaluable method of demonstrating the point to the jury. Cell site evidence, when not presented in an impactive way, can be confusing in court – and at worst, can overwhelm those sitting on the jury. This was an elegant, easily understandable piece of evidence – and it worked.
This enhanced service was agreed by collaboration of the cell site expert with the customer force at the initial case conference. This has shown the value of providing expert advice from the start of the analysis.
The power of the evidence more than justified ‘going that extra mile’ – and it ultimately saved the expense of carrying out at least one additional survey. I hope this goes to show that a tailored investigation, based on the intelligence of the case and the requirements of the investigating officer, can be a much more powerful approach than a ‘one size fits all’ turn-up-and-survey approach.
If you would like more information about cell site analysis and its use in cases of this type, please contact me or any of my colleagues by emailing firstname.lastname@example.org. As ever, please keep the feedback to these articles coming in. We do enjoy reading your comments and opinions.
Keep posted as next month we will look at another aspect of cell site that will make or breaks a prosecution.