Monday, November 17, 2014

Cell Phone Tracking via Call Detail Records

We live in a world today where individuals’ movements and locations are being recorded in many different ways.  These movements and locations are commonly being used as evidence in civil, criminal and domestic litigation.  It is of paramount importance that anyone who is involved in litigation that uses cellular location evidence understands the appropriate and inappropriate use of this type of location data.

Recent decisions by some courts have made it possible for government agencies to obtain real time tracking information using an individual’s cellular phone or other cellular device without having to show probable cause or obtain a search warrant.
Additionally, the government and courts continue to maintain the position that obtaining historical call detail records for an individual does not require probable cause or a warrant since the person holding the cell phone is voluntarily providing their location data to a third party, namely the cellular service provider.  However, obtaining real time geo-location of a cell phone via the emergency 911 (E911) system in many cases requires either a warrant or permission from the cellular carrier.

What is Cellular Data Analysis?

Cellular data analysis is the process of collecting, analyzing and presenting the approximate location of a cell phone or other cellular device based on data obtained from the wireless company or in some rare cases, from the device itself. 
There are several types of cell phone location data that can be collected and examined;
·       Carrier based location data is collected by obtaining historical call detail records for a particular phone from the cellular carrier along with a listing of the cell tower locations for that carrier.  This data is then analyzed for the purpose of generally placing a cell phone in a location on a map.  This is NOT triangulation.
·       Cellular data  in the form of “pings”, which is  real time geo-location tracking of a cellular phone or other cellular device by activating the emergency 911 system (E911), which will then use either a network based or handset based method for locating the phone and will provide a location estimate generated via triangulation of the phone handset.
·       Law enforcement may issue a warrant or use an exigent circumstance application to get real-time call detail activity for a phone.  This is the same type of data contained in a historical call detail record but is provided in real time.
·       Cellular data may come from the device itself in the form of GPS location data either from an application running on the phone, a geo-tagged picture or some other data point.
It is important to understand about geo-location of a cellular phone or other cellular device is that the accuracy of the geo-location is dependent on a number of factors, not the least of which is the ability of the analyst to properly interpret and present the data and the methods used to present the information.

How is Cellular Data Analysis Used?

Cellular data analysis is used quite often in criminal cases to attempt locate a person of interest, either as they go about their criminal enterprises, or in relation to a particular incident or crime.
This type of analysis is also used in civil litigation involving vehicle accidents, property damage claims and other types of cases where the location of a particular cell phone at a particular time is of interest.

What about Triangulation?

The term triangulation is often misused and applied to the analysis of historical call detail records.  Call detail records only contain information about a single cell tower that was used when a call was made.  To triangulate the location of any phone or object you have to have a minimum of three points or more of reference.

Is There an Accurate Way to Track a Cell Phone Location?

Yes, but it can only be done in real time by using the cellular system or the cellular phone’s GPS unit to track the phone.
There are basically three ways to locate a phone using technology:  Handset based GPS, network based triangulation and hybrid location.
By law, cell phones are supposed to contain a GPS chip for the purpose of locating the phone in an emergency.  However, even today, not every phone has GPS capability. 
The most accurate way to locate a phone is by activating the phone’s on board GPS unit and allowing that to provide the phone’s location back to the wireless company for transmittal to authorities.  Handset based GPS location is supposed to be accurate within 50 feet. 
The second way to locate a cell phone is by triangulating the phone using network based location services.  What this does is calculate the position of the cell phone relative to three or more cell towers using round trip delay, and provides that location information back to the wireless company.
The third way to locate a cell phone uses a combination of network based triangulation and local wireless router locations.  However, this is not in common use to the best of my knowledge at this time.
When a cell phone user calls 911 on their cell phone, the 911 operator will get a cell tower location, a sector and in some cases a GPS location for the phone.
However, these locations can be off up to several thousand feet from the actual location of the phone.  In order to make sure that the GPS location is as accurate as possible, the PSAP (Public Safety Access Point) operator should manually update the location from their terminal.

Is cell tower tracking evidence junk science?

Generally locating a cell phone based on its historical call detail records for towers used at particular dates and times is an acceptable method and is based on the simple fact that cell phones do connect to cell towers .  From that standpoint, it is not junk science. However it is a science that is easily misinterpreted and misstated when prepared and or presented by persons not qualified to do this type of analysis.  The concept of plotting the locations of cell towers on a map is simple.  Understanding and explaining the underlying technical issues and considerations is extremely complex.

Is there a good use for cellular location evidence?

 Properly applied and interpreted cell phone location evidence can be helpful in many cases.  The issue is the overstatement of the accuracy of the phone’s location.
For instance, if the phone is using a cell tower in a particular town where an incident occurred and the person who was in possession of the phone claims to have been in a different town, it is a simple presentation to dispute the person’s claim.
Another good use is for tracking a phone across a distance based on cell tower usage.  While the analyst cannot claim a particular road was used, the cellular evidence can certainly illustrate for a jury that the phone did in fact travel from one city to another or some area to another.
In a recent case cell tower evidence was used to show that a phone call was made near the location of the defendant’s home and a subsequent call was located near his place of employment.  At issue was whether or not it would be possible for the defendant to travel to another location, commit a burglary and still make it to the location near his work in the time span between the calls.  By combining the cell phone locations, time estimates from Google Maps and the location of the burglary, the jury was convinced that the defendant could not have committed the burglary and still made it to the location of his work in rush hour traffic in Washington, DC.
Cellular evidence can also be used to show that a phone was near a particular area of interest with some reasonable confidence.   And with more data points, this kind of analysis can be helpful in showing that even if the analyst cannot determine why the phone picked a particular tower, dozens of uses of the same tower in a short time would lend itself to showing that the phone was using that tower over other towers nearby on a consistent basis.
The other side of cellular evidence is the use of call detail records to show communications via voice, data or text in the context of a timeline.  In a recent case involving a tractor trailer truck involved in an accident it was clear from the call detail records that the driver was not using his cell phone near the time of the accident for phone calls or text messages.  The issue for the attorneys who brought in an expert in the case was the time stamps on the cell detail records.  Initially it appeared at the times for the phone calls were within minutes of the accident.  However, once it was determined that the time stamps were dependent on the time zone of the cellular switch used to handle the call, the time was over an hour prior to the accident.  In this case, the truck driver was in the Eastern Time zone when the accident occurred, but the switch that processed the calls was in the Central Time zone and some of the calls reflected the time from the switch. Once the time stamps from the call detail records were moved an hour earlier, the issue was resolved.

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