Using cell tower data to track a suspect’s location

With the recent U.S. Supreme Court decision Riley v. California, the topic of cell phone forensics is on the mind of many attorneys. Cell tower location tracking is a related area where investigators gather information about a cell phone’s location using data from cellular towers contained in phone records. Attorneys should be aware that location tracking through cell tower data is a questionable practice, as explained in these recent articles in The New Yorker and The Washington Post.

How its proponents say it works:

Proponents of cell tower location tracking explain that when a phone call is made through a cell phone, the phone sends out a radiofrequency signal to the “nearest” tower. Investigators will look at phone records to see which tower the phone connected to at a specific time. Once they have located the individual tower that facilitated a particular call, investigators will determine the geographical range of that tower and conclude that the phone and therefore the person using the phone were within that tower’s range at the time the call was made. Triangulation or the use of three different calls or cell towers to create an overlapping area similar to a Venn diagram that produces a smaller potential location, is more reliable than the single tower method. However, triangulation data or GPS data (which could potentially give an exact location) often is not available. Police frequently trace the phone call, find the tower, determine its range, and see if the suspect’s cellular phone data places him at or near the crime scene at the relevant time.

Limitations of this technique:

Cellular communications experts explain that tracking a phone’s location based on its connection to cell towers is not so simple. The proposition that a cell phone will connect to the nearest tower is not accurate. There are many complex, proprietary algorithms that a cellular company’s control center uses to decide which tower gets the call. Cell towers’ ranges can vary from several square miles in urban areas to in excess of 20 square miles in rural areas. Geography, network congestion, weather, height of the tower, and many other factors can affect which cell tower picks up a call. For these reasons, claiming that a person is within a specific radius of a certain cell tower is not possible with the current technology.

Misuse of this evidence:

On May 28, 2014, Lisa Marie Roberts was released from prison in Oregon. She had been in custody since pleading guilty to manslaughter in 2004. When Roberts’s trial attorney learned that the state’s evidence included the pinpointing of Roberts’s location at the time of the crime using cellular tower data, he urged her to take a plea. The prosecution claimed that Roberts’s cellular phone records placed her specifically in Kelley Point Park at the time they believe the victim’s body was dumped there. Investigators used the aforementioned technique of tracing phone calls made by Roberts that day to show that not only was her alibi not credible, but also that she was exactly in the location where the body was found. On appeal, the defense’s expert testified that the notion that the nearest tower to a cell phone is per se the one that facilitates the call is not testable, reliable, or provable science.

The appellate court decided that it was because of this flawed evidence that the trial attorney encouraged Ms. Roberts to take the deal, without which she would not have plead guilty to a crime she says she did not commit. This myth of the police’s ability to track missing persons or suspects by their cellular phone by using only single tower data is commonly accepted and unchallenged by defense counsel. Attorneys should consider consulting with a cell tower forensics expert to determine the reliability of this evidence and whether this evidence can either locate the defendant at the scene of the crime or support an alibi.

To read Ms. Roberts’s granted Habeas Corpus Motion for Ineffective Assistance of Counsel, click here.

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