Adnan Syed — Integrity in Testimony
by Rick Zemlok
The analysis of cellular phone evidence came to the forefront during a “Serial” podcast, which documented the 1999 murder investigation and ultimate conviction of Adnan Syed. “Serial” drew attention to the alleged unreliability of cellular phone records. The point of this article is not to counter the defense of that case, rather to educate you as a consumer, member of society, and potential juror, on the content and reliability of such records in 2017.
There are many myths behind phone records so let’s discuss the facts.
Historical cellular phone records, commonly referred to as call detail records (CDR’s), are stored by a service provider (i.e., AT&T, Sprint, T-Mobile, Verizon, etc.) for typically six months to two years. They include a range of information to include billing data and call details such as date, time, duration, calling number, called number, call type (i.e., voice/text) and cell tower location information. Often, carriers provide investigators with CDR’s listed in various time zones, depending on the location of the caller, where the provider company resides, or a general use of universal time code (UTC). An untrained investigator can easily misinterpret these records if they do not fully understand the details for each service provider.
Historical CDR’s can be critical in providing an investigator information that may help identify suspects, discount persons of interest, support physical evidence or refute suspect statements.
So what’s really important? How reliable is the location information in CDR’s in determining the location of the actual phone at a given time? Is there a difference in accuracy when comparing the cell tower the call started on compared to the cell tower where the call terminated?
There’s actual process, which may seem complicated to the laymen, of determining the actual location of a cell tower and the coverage area it has. But essentially, one can determine GPS coordinates for a cell tower from the information provided in the CDR’s which allows you to pinpoint its location on a map. These cell towers are typically divided into three sections, but can come in other configurations as well. Boring, but necessary to understand, particularly when a person’s guilt or innocence may weigh in the balance.
Once the investigator has determined the tower’s location and sectors, it’s important to understand it’s actual area of coverage. Now this is the tricky part and the one that can get investigators into trouble and the one that defense experts like to greatly exaggerate to draw doubt within a jury. Again, skipping a bit of technical expertise, but the very basic idea is that a cellular network is made up of multiple cell towers that provide overlapping coverage. The purpose of this is to make sure that you don’t drop your phone call when you are driving or moving around.
Each cell tower will have an area within the network where it provides the strongest and best signal, which is communicated to all the cell phones from this carrier that are in the area. The cell phones are constantly being monitored by the network to allow a call to be made or received and ideally will connect them to the strongest, best signal. The strongest, best signal is typically the cell tower in closest proximity to the actual phone. However, there are a variety of factors that come into play such as buildings, physical obstructions, network traffic, etc. Though these factors can play a role in cellular coverage, it is a common misrepresentation to claim the cellular network is completely unpredictable and the coverage of a cellular site can’t be narrowed down further than 15 square miles in an urban city (good try defense expert).
Will the coverage area of a cell site sector be a neat little 120-degree pie slice? No, unfortunately, it’s not that quite that simple.
Due to the various complexities in cellular network performance, especially when analyzing data from the past, contemporary law enforcement needs a way to overcome the courtroom battle between experts and their training and experience. Don’t get me wrong, this is a huge factor for any subject matter when it comes to testimony. But what if there was a better way? A way to show actual coverage, using tested and certified equipment that can provide repeatable results? More importantly, something simple enough that law enforcement can use and understand without an engineering and cellular theory background.
Now there is. Specialized equipment long used by cellular engineers can now be used by law enforcement to not only collect the geographical coverage area data but also to correlate it to the information provided in call detail records. While there are a few companies producing such equipment, my experience lies with a company called Gladiator Forensics. Their product, the Gladiator Autonomous Receiver (GAR) is a backpack-sized device that can be taken along in a vehicle and driven around a crime scene or an entire city. GAR collects the data being transmitted by each service providers cell towers in the area, in two-second increments and sends this to a server where it correlates with existing cell tower data from the provider.
This technology allows investigators to visualize and depict on a map the actual cell tower locations, sectors and displays the two main types of cell tower coverage which are known as dominant coverage and possible coverage.
Dominant coverage is the area where the cellular tower and sector in question provides the strongest, best signal. A cell phone within this coverage area is highly likely to begin a call on this cell tower and sector. Once a call is connected, the network can allow for the call to be handed off to a nearby cell tower if conditions such as network traffic are present. So when comparing beginning cell tower connection to ending cell tower connection, the beginning is actually the more reliable indicator of location.
Possible coverage is simply the geographic area where the signal from the cell tower and sector in question has a strong enough signal to handle a call. The possible coverage area is obviously bigger than the dominant coverage area. Anything outside of these two types of coverage areas doesn’t have the ability to handle a call from the cell tower and sector in question.
What does all this mean? This highly specialized equipment allows investigators to provide scientific evidence to show actual cellular network coverage and helps eliminate concerns on both sides of the table regarding assumption, manipulation of data, and exaggeration. It replaces opinion with fact and serves to allow investigators and prosecutors to present professional evidence free of prejudice.
Going back to the question raised in the “Serial” podcast (without debating the records of that case), in 2017, is the cellular site data that is present both at the start and at the end of call reliable? Yes, and more so than ever!
