Cell site blog: ‘consistent’ data, or data ‘not inconsistent’

By Dr Iain Brodie, Senior Cell Site Expert

As cell site experts we are often asked to consider whether cell site data is ‘consistent’ with a specific scenario, in the knowledge that our words can have a significant impact on how a jury thinks.

For example, a typical question put to us might be:  is the data for a particular mobile phone ‘consistent’ with it having been at the scene of a particular incident which occurred, say, in the centre of Birmingham at 12:00 on a particular day?

If the cell site data for the phone shows that it connected via a cell site in the centre of Birmingham which serves the scene at 12:00, then in my opinion it is clear that the data is consistent with the phone having been at the scene. This does not mean that I think the phone necessarily WAS at the scene, as the cell ID used will cover an extended area and, of course, locations that are not the scene. Given the unpredictable ways in which phones are used, however – what data there is supports the contention that the phone was at the scene.

The situation is equally clear cut if, at 12:00, the phone connected via a cell in central London. It is physically impossible for the phone to have connected to a cell in London whilst located in Birmingham, so (if the records from the network are correct) such data would be in conflict with or inconsistent with the phone having been in central Birmingham at 12:00.

If, at 12:00 and 12:01 say, the phone connected via cells in central Coventry, the scenario is slightly different. It is not, under all circumstances, physically impossible for the phone to have connected to a cell in Coventry whilst located in Birmingham. But in all normal circumstances – given the huge number of other more likely cells in Birmingham for the phone to have used, I would still say that this data was in conflict with the phone having been in central Birmingham at 12:00. Such an opinion could be reinforced by carrying out further work if required, but in general such further work would not be required.

But imagine the data was less clear cut. For example, now my phone’s call data records show a cell site in Coventry connected to by the phone at 11:00, a cell site in Solihull at 11:30, a cell site in eastern Birmingham at 11:45 and a cell site in Wolverhampton connected to at 12:30.

In my opinion this data is again ‘consistent’ with the phone having been at the central Birmingham scene at 12:00, as the logical journey of the phone would have been close to the scene. Indeed there are not many plausible routes other than the phone passing close to the scene at 12:00 that could generate such data – although again, I do not believe the data means that the phone definitely was at the scene (and nowhere else) at 12:00.

If, however, the call data for the cell in Wolverhampton was not so. All we would have was call data consistent with movement of a phone towards the centre of Birmingham, but even less evidence that the phone was in the centre of Birmingham. Such a scenario presents quite a grey area for evidence of opinion. Some experts may say the data is still consistent with the phone being in the centre of Birmingham at 12:00, whilst it may be argued that there is, in fact, NO data consistent with the phone being in the centre of Birmingham at 12:00.

I would say that the data is consistent with the phone having travelled towards the centre of Birmingham in the times leading up to 12:00, although there is no data showing it had been used in central Birmingham.

A final scenario would be where the phone connected to a cell site in Coventry at 11:00 and again to the same cell site in Coventry at 12:45. In this scenario it is quite POSSIBLE that the phone had time to travel to the centre of Birmingham and back, but there is no data that would lead me to expect that this had been the case. Here I would use the phrase ‘the data is ‘not inconsistent’ with the phone having been in the centre of Birmingham at 12:00 but there was no data indicating it had done so’.

This may seem like semantics. However, in a case where I gave evidence for the defence earlier this year (in Birmingham Crown Court as it happens), the prosecution expert asserted that there was cell site evidence ‘consistent’ with the defendant’s phone having been travelling away from a location of a crime at a particular time, when the cell site used for all of the relevant calls provided service at his home address. The prosecution expert’s use of the word ‘consistent’ here was challenged and the challenge was accepted by the court.

The judge, Justice John Royce in summing up said:

‘although the data is not in conflict with such a theory <that the defendant was at the relevant scene>.  The data <for the time in question.> is not consistent with being at the site.  It could possibly be that the phone was en route however from the site to the defendant’s home…’

the prosecution has been driven to trying to construct theories because of the absence of solid evidence.  They have tried to make bricks with but a few straws, and have done so with admirable skill and ingenuity.  But is this sufficient evidence to be left to the jury?  Could a jury, on this evidence, properly directed, safely convict?  The conclusion to which I am driven is that they could not. Accordingly, I shall direct the jury to return not guilty verdicts’

Had the prosecution expert’s semantics not been challenged, the outcome may have been different resulting, possibly, in a miscarriage of justice.

July 2012 cell site blog: The top five (potential!) pitfalls in cell site analysis.

By Nicholas Patrick-Gleed, Cell Site Analyst

This month’s cell site blog takes on a slightly different style.  The team here at CCL-Forensics has been discussing the most common potential pitfalls encountered in the world of cell site evidence, and thought it would be a useful exercise to commit some of them to the blogosphere.  So, rather than focusing on a particular topic, we’ll look at the top five (as we see them) issues which need to be at the forefront when planning and, more importantly, carrying out a cell site investigation.

We’ve touched on some of these in previous blogs, but they form a concise summary of some of the ‘issues’ we have seen experts (almost) experience.

This Month’s Topic: Five things to be wary of in cell site analysis

1. Exhibits without interpretation

When working for the defence, we regularly see prosecution evidence which can best be described as “exhibits without interpretation”.  A good example of this is a series of maps plotted by an intelligence analyst, who has carried out a series of instructions based on some call data records, but presented them without any explanation of what they mean.  This not only causes confusion and delay within the criminal justice system (the defence will, no doubt, ask for the explanation at some point – so it may as well be provided at the outset) but also means that an opportunity could be missed as part of the investigation stage.  Simply ‘blindly’ plotting information on a map is hardly investigative – but we have seen it more than once.  What is the point of an exhibit without context?

From the prosecution’s perspective this is an obvious potential pitfall – as it means that the evidence does not include something which could enhance the prosecution’s case.

There have also been occasions where the defence leaves it until the 11th hour before ‘complaining’ that the person who has produced the exhibit is not an expert – and the judge could rule that the prosecution needs to carry out more expert analysis.

It’s simply not worth chancing these situations.  Moral of the story: produce exhibits which mean something; it makes for a smoother investigation.

2. Who’s who on the call data records?

Cell site is full of idiosyncrasies.  It’s what keeps us experts on our toes.  But there are small variations between networks and circumstances can lead to major confusion.  The best example of this is when you are analysing a call data record, and the person is in contact with someone on the same network.  There are occasions when both parties cell IDs appear on the same CDR – which can immediately confuse things.  Furthermore, and lets use the ‘3’ network as an example here, if an incoming call to the subject phone is unsuccessful, then the cell ID for the person making the call still appears on the CDR.  This is particularly a problem, as the CRD doesn’t differentiate between the A and B phone (in columns) and so this needs to be taken into account.  It’s pretty easy to spot if there’s a day’s worth of cell IDs in London, and one in Edinburgh – but when both parties are geographically close, then vigilance is the watchword.

This is especially the case if the person plotting the calls is not trained in these nuances – as they may easily go unnoticed.

Moral of the story: be thorough.

3. Timely surveys

Networks change and evolve.  Nothing new there, but the sooner the survey is carried out after the incident in question, the better.  It means the results will be more accurate and better reflect what happened.

We previously touched on our use of historic data, which may help to counteract this problem – and this is a benefit of the robust methodology which CCL uses.  But, timeliness is still a big potential pitfall for a number of reasons.

One of the biggest is the evolution of “Everything Everywhere” – or the merger of
T-Mobile and Orange as most people still know it.  This means that “Everything Everywhere” now has many more channels available than each of their competitors – and consolidating cells seems like a sensible thing to do.  If there are two cells covering the same approximate area, it seems only prudent to use just one of them and either deactivate the other, or reallocate it to, say, the new 4G networks, which have been in the news recently.  This clearly impacts on the survey, especially if the cell in question is no longer transmitting.

Moral of the story: Consider the impact of the T-Mobile and Orange merger before surveying.  What are you expecting to see – and what are you expecting NOT to see?

4. Getting the whole picture – not just a small slice

Cell site is all about focusing on a phone’s movements around the time of a crime, right?  Wrong.  Yes, this is often the best place to start, but it can also be vitally important to look at the patterns of usage within the data as a whole, rather than just isolating and concentrating on a small piece of evidence.

There may be no evidence of a phone being in an area of interest at a particular time, but the best advice here it to stop, look around and think.

There may be behaviour patterns, where the time in question shows some deviation from the norm. There may be evidence elsewhere of the use of ‘clean’ and ‘dirty’ phones.  There may be evidence someone ‘casing the joint’ before the crime, which goes against the usual pattern of usage.

One just doesn’t see these when points are blindly plotted on a map.  The solution is to have as much data available as possible at the outset of a cell site assignment (or as much as can be reasonably requested under RIPA).

At the end of the day, it depends on what question you are trying to answer, but the moral of this story is: Don’t just rely on data from the time of the incident.  More complex investigations need more data.

5. Surveying techniques

Quite honestly, this is something of a bugbear of ours, and a topic which we have covered numerous times.  With that in mind, I won’t go into any major detail, but just summarise something which we think all cell site experts should adopt.  (And we’ve had this published in a peer-reviewed journal, so it’s more than just a passing fad!)

Movement is key to getting an accurate overall picture of how a phone interacts with cells.  The concept of ‘dragging’ a cell can be key to determining if a cell provides coverage at a location.  Driving to a location from a number of directions can result in a different cell providing coverage, depending on which direction you arrive from.  This is because the phone has a tendency to “hold onto” a cell, rather than chopping and changing – (to reduce the risk of a dropped call).  Spot samples (i.e. turning up at a location, surveying without moving, and then leaving, is hardly comprehensive).  This is about so much more than simply dotting the i’s and crossing the t’s.

While we’re on the subject, it’s worth touching on tracking frequencies.  Network Operators, typically use two or three 3G frequencies at their cell sites.  When moving geographically, a phone may use a new cell which uses a different frequency than the original one.  This created a potential pitfall when surveying, as the expert needs to be mindful of how many frequencies are available, and ensure the most appropriate survey is therefore carried out.  The moral of this part of the story: remember there is more than one available frequency – and be as thorough as the investigation requires.

I hope you’ve enjoyed our whistle-stop tour through the potential pitfalls of cell site analysis – and as, ever, we’re always keen to hear your thoughts on the matter.  If you would like to discuss any aspect of cell site analysis, please don’t hesitate to drop us a line at cellsite@ccl-forensics.com

Next month

Next month, Dr Iain Brodie analyses comments made by a judge during a recent case, and highlights what the criminal justice system REALLY wants from cell site experts.

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

A puzzling cell site case

This month’s cell site blog takes a look at an obscure case involving international roaming. Dr Iain Brodie tackles an unusual occurrence involving breaking and entering.

Call data records were supplied, but they showed an unexpected pattern of calls which would leave even the most experienced cell site analyst baffled.

This is featured in the case study below. If you require more information, please feel free to get in touch on 01789 261200 or email ibrodie@ccl-forensics.com.

Case study: An unusual international roaming scenario

CCL-Forensics’ cell site analysts recently carried out investigations for a case from about a year ago in which the suspect was accused of a spate of breaking and entering.

I was initially very puzzled by the call data records for the suspect’s phone, some of which are reproduced below:

Unusual call data activity

As you can see, the call data records appeared to show some very rapid movement of the suspect’s phone – including international roaming. After further analysis, we had to admit that we were a little stumped.

However, ANPR data was subsequently for the suspect’s vehicle was subsequently made available to us. This, together with some eyewitness reports, made the case much clearer and we were able to piece together what had happened, and identify the culprit.

Take a look at the ANPR data below to find out what had happened.

Continue reading

The idiosyncrasies of mobile phone network providers

All mobile phone network providers have to, by law, hold call data records for at least one year. Problems arise, however, because they all present the records in very different formats and some of the data can seem irrelevant and confusing, giving rise to the risk of information being misinterpreted.

Call data records?

CDRs are similar to itemised phone bills – but they hold much more information. As well as the dates, times and numbers called, CDRs also include IMEI numbers, cell site data and locations.

What do you mean by idiosyncrasies?

Here’s an example: some networks will record the cell ID (the sector of the phone mast) for phone calls which were made, but didn’t connect – others won’t. And some will give the other party’s cell ID if they’re on the same network. This provides a number of opportunities, but these idiosyncrasies also present significant risks if the person analysing them isn’t aware of all these nuances.

As mentioned in a previous blog, the key is to get the call data records into a workable format. This is a massive data manipulation exercise, compounded by the fact that the networks can record locations differently – they may use the postcode, BNG (British National Grid) or latitude and longitude co-ordinates – plus the other idiosyncrasies mentioned above.

Another major issue is that CDRs from some networks’ CDRs can apparently attribute the cell site data from the person at the other end of the call to the subject phone. An unwary analyst may misinterpret this data as coming from the person receiving the call by inadvertently associating the outgoing data with incoming calls and vice versa. This is something I have even seen in court.

Shown below is an example of part of a call data record for phone 07875 477828 for part of 03/12/2010.

Note that the call at 20:54 appears to show cell site information for the phone number 07772 000987 even though this number was not the target of the call data records. An amateur assessment of the call data records – simply looking at all the cell IDs – might conclude that the target phone 07875 477828 had been in the service area for cell
03010 52339 at this time. Such a conclusion would be totally false.

This cell was many kilometres from a particular location of interest in a criminal investigation in one case. Had this issue not been picked up in court, it could easily have led to a miscarriage of justice.

Call data record

Example call data record

What other oddities are thrown up by CDRs?

There are a couple of fairly common issues that can cause problems for even the most experienced analyst.

Text messages may appear on the CDR that the user isn’t aware of. They do exist – but are likely to have been network messages which the user doesn’t actually see. They are “codes” sent by the network under a number of different circumstances to update software, and user details – amongst others. These texts can also be indicative of the user taking the SIM card and/or battery out of the device.

They are not a particularly common occurrence, but can provide additional useful evidence especially if a suspect has deliberately not used their phone in order to stay off the network. For example: a suspect may put a new SIM card into a device at their home, unaware that the phone is then communicating with the network, and therefore leaving location data on the CDR.

As mobile phones become more complex, and smartphones begin to dominate the market, this also provides a useful opportunity for cell site analysts. Not only are calls, texts and network messages registered on the CDR, so is data packet transmission. Every time the phone connects to the internet, whether browsing the web, social networking or being used by apps, this is also recorded. However, unlike a phone call, which records the start and end cell, this data will show the cell ID for where a user started browsing, but not necessarily where they finished.

It gives rise to another question: how long is a browsing session? Some networks record browsing sessions in blocks of time – for example, the cell ID of a session begun at the start of an hour will be recorded – and that will also include a second session begun at the end of that hour. Both locations may not necessarily be separately recorded. This issue again is shown on the call data above at 22:00 and 23:00.

How can the problems caused by these idiosyncrasies be avoided?

There’s no substitute for experience. Cell site analysts with substantial knowledge of these idiosyncrasies can easily circumvent any problems – by spotting them up front.

In addition, converting and sorting the vast amount of data into a properly formatted call sequence table (CST) makes the data uniform and easy to work with.

The CST means that investigators can filter and delete unwanted data easily and without the risk that something will be missed.

CCL-Forensics has developed a tool which takes raw data from the network providers, and converts it into a consistent, workable form – removing the need for extensive manual manipulation. For more information please feel free to get in touch on 01789 261200.

Most importantly, analysts really need to know the individual networks well in order to understand their various oddities and work around them.