Cell site blog – Never mind the quality, feel the width

Thoughts and observations on how ‘more’ could mean ‘less’ in the presentation of cell site analysis.

By Matthew Tart, Cell Site Analyst

This month – we look at quality over quantity in cell site analysis – with particular emphasis on a recent example where a pile (literally) of maps could easily have left jurors’ heads spinning.  And cost the prosecution a considerable sum.

This month’s topic: Getting the balance right in cell site analysis 

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.

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 cellsite@ccl-forensics.com

Benefits of hindsight: Why ‘nurturing’ data can prove valuable for cell site analysts.

It’s at this time of year, when the sun is shining (well, it IS at the very moment these words are being written), that carrying out an intensive cell site survey seems almost like a perk of the job. But, as everyone involved knows, a cell site expert shouldn’t expect that each assignment should come with such luxuries.  Surveys aren’t always necessary – and even where they are, there could be a smarter solution.  In this month’s cell site ‘blog’, Matthew Tart looks at the possibility of using data from previous cases.

This month’s topic: Use of historic cell site data

Q: First of all, precisely what do we mean by historic cell site data?

A: Simply, it’s data CCL-Forensics has generated from carrying out previous cases, which we have organised and stored in an ever-growing database.  The reason we have this, is because we don’t carry out static surveys as we have found they have limited repeatability and failed validation (this is described in our previous blog here), which I’ll go into in a little more detail later.  So if we’re interested in where a particular cell serves, there is a potential that we’ve already surveyed relevant areas.  We’re not (quite!) up to UK wide coverage yet, but the database is growing rapidly, plus we’re getting additional cell data every time we travel between our offices and the general area of the survey.  

Q: So, how does this actually benefit the case. Surely, all cases are different, and you may still have to do some surveying?

A:  This is not necessarily a replacement for any future survey, it is an enhancement, but it does have some significant advantages.  The first being that it can help us to scope out a case, and therefore produce a more accurate strategy – keeping costs down.  The more CCL-Forensics know about the network infrastructure of the location in question, the more easily we can produce the most cost-effective forensic solution to the problem at hand. It’s also been useful in court, where very specific questions have been raised about the coverage of a cell; if we have relevant data, our expert in the witness box can easily (and with no cost to anyone involved), use that area information – adding value to proceedings.  In short, it means that we simply have more data with which to work – and scientifically, that’s a very good place to be.

Q: But isn’t there a risk that the data may be out of date?

A: The timeliness of data is always a consideration in cell site analysis.  One of the most common concerns tends to surround how the network may have changed in the (often) months between the incident and the survey.  By using data collected in the past, it could be more relevant to the time of the incident.  Additionally further surveys can be undertaken to assess whether that there have been changes in the network over a period of time – and not even the networks themselves can give us information as reliable as that.

Q:  Why aren’t all cell site analysts doing this?

A: I’m not saying it’s only CCL-Forensics who are doing it, but there are analysts who practice certain surveying techniques where keeping a database would not be appropriate.  Earlier, I mentioned the concept of carrying out static surveys.  CCL-Forensics have gone through this at length before, but this just goes to reinforce why turning up at a scene, carrying out a few measurements and then leaving again, is not the strongest piece of science in the world.

Using static surveys each job stands alone and in isolation from any other examination.

Q: It must take up a serious amount of storage space

A: CCL-Forensics had to buy a huge new server to hold this data, but it’s already been worth it.  We’ve saved so much time by having access to this data, and passed on significant cost savings as a result.  It also means that our clients are getting stronger evidence, effectively for free.  It’s stronger because we can more accurately assess service areas, and also get an educated idea of network changes, which can inform expectations at the outset of an investigation and same time during it.

For us, it’s definitely an investment in the future and ideally, we’d like to be a position where we have the whole country mapped, but that’s a little way away at the moment!

To finish with an example: There was an urgent pre case management hearing relating to an incident in a city 150 miles from our base.  We were asked to provide some analysis of call data records on a Wednesday morning, which were needed by the Thursday evening. 

CCL-Forensics checked our database and found extensive surveys in and around the locations of interest, and could make an informed estimate of cell service at those addresses without the disruption, delay and cost of travelling to the area and carrying out a survey.  Basically this would not have been possible, given the time constraint, had we not had the historic data. 

Of course it is not just the survey time that causes delay, it’s the preparation, travelling, data manipulation, analysis and reporting of that data.  But, as we’d already surveyed the area, the client had the report they needed well ahead of the deadline: something which would have been practically impossible otherwise. 

To summarise, every case we do makes CCL-Forensics service stronger.

For more information about historical cell site data usage, or any of the other issues highlighted in this month’s blog, please email Matthew Tart at mtart@ccl-forensics.com or call 01789 261200