By Matthew Tart, Cell Site Analyst
This blog starts with a case we were involved in recently, involving a high profile crime with a number of defendants. On this occasion we were working for the defence, but this story acts as a useful pointer for the prosecution by illustrating techniques that experts used by the Crown should - and should not - be doing. We'll focus on a method used by a large number of cell site analysts (but not ourselves) which is not necessarily robust or stand up to close scrutiny.
This month's topic: Getting the balance right in cell site analysis.
Q: What were the details of the case?
A: The prosecution were investigating the probability of a suspect being at a crime scene – a pub in an inner city location. At the time of the crime, one of the suspects (we were working for that suspect's defence solicitor in this case) made a phone call. The call data records showed that this phone call was made on what we'll call 'cell A', which was on a mast near the crime scene – but also near to his home address which was about 500m away.
The suspect's alibi was that he was at home at the time of the crime and the phone call.
The prosecution's outsourced expert carried out 'spot samples' (i.e. turned up at a location with a piece of equipment) at both the crime scene and the alibi location. Their report showed a different cell serving at each location. Cell A was shown as best serving at the crime scene – but not at the alibi location.
Q: So what did we do differently?
A: We carried out a much more extensive survey i.e. a drive survey at the home address and the surrounding area. This was carried out with regard to the cell of interest (Cell A), and we used multiple pieces of equipment and repeatedly moved in and out of the area. We found that cell A provided coverage north, south, east and west of both locations (crime and alibi scene), and based upon this, could not distinguish between the mobile phone being at either location. The evidence was simply not strong enough to suggest one or the other.
Q: So, were both sides saying something different?
A: Yes and no. Before the court date, the prosecution's outsourced expert asked for a copy of our defence report, which we provided. We then discussed the contents with the expert over the phone, who claimed that he wouldn't expect cell A to provide coverage at the home address. After looking at our evidence, he admitted that our assertion that the cell served at both addresses was actually the most valid interpretation of the evidence. This is a worrying admission/u-turn to say the least. This is despite his evidence not documenting that cell A also serves at that crucial home address.
Q: The other side claimed that a different cell provided service at the home address. Did your survey find that cell as well?
A: Yes, but we found four cells which served at the home address. Cell A, the one the other side claimed – AND two others.
Q: How was this data presented by the prosecution's expert?
A: In a rather cumbersome, and lengthy fashion, to say the least. There were a number of suspects, and their report showed the same maps over and over – and over – again. It showed the locations of interest, calls for varying time periods, and whether the cells used actually covered the locations. This came to more than 100 (one hundred) maps. All printed on A3 paper and bound into a daunting, unwieldy piece of physical evidence, which the jury would have to absorb.
I would defy even the most attentive juror to have easily made sense of this massive tome. Notwithstanding the threatening size of the document, but all the pages were practically the same, or almost identical copies of other similar pages. You simply wouldn't be able to take it all in. Especially as one wouldn't expect jurors to be familiar with this type of evidence – making it all the more crucial to have it presented in a friendly form.
Q: What would we have done differently?
A: Firstly, not produced a huge weighty un-jury-friendly document. The best way of presenting this evidence (for which we would have had MUCH more survey data, having done more than carry out simple spot samples) would have been a series of two or three detailed maps which can be presented interactively at court with the relevant points being highlighted by the expert in the course of presenting the evidence. These maps would have covered specifically the period of interest – and would have a secondary, financial, benefit.
By not producing hundreds of maps, we would have saved a considerable amount of time – and therefore cost. We would estimate that producing this unmanageable number of maps and documents would have potentially cost tens of thousands of pounds. Our approach would almost certainly have been cheaper AND more robust.
Q: So the lesson here is...
A: ...to think about what you need to achieve, and the best way of doing it. Don't be held to ransom by an outsourced experts 'way of doing something'. Hopefully this example has shown two things. One, that carrying out spot samples (as we've mentioned in previous blogs) may not be the most appropriate way of surveying. And secondly, that the end product i.e. what the jury see and have to understand, can be something a little more sophisticated than a batch of similar-looking, repetitive - and quite frankly, uninspiring – maps and tables. Technology has moved on. So has cell site analysis. And so has the presentation of evidence in court.
In terms of maps it is quality not quantity that delivers the most impactive conclusions in relation to the possible locations of a mobile phone.
For more information about this – or any aspect of cell site analysis, please contact Matthew Tart (or any of our other cell site analysts) on 01789 261200 or by emailing firstname.lastname@example.org