In an article by The Economist, Larry Daniel of Guardian Digital Forensics–an expert our firm consults with regularly–noted that cell phone tower data, which is used to identify the location and movements of a suspect at a given time in the past, is often misinterpreted. That is, the conclusions drawn by police (or defense lawyers) about what the data means is often mistaken, and the data may not prove that a particular suspect was in a particular location.
For example, law enforcement officers often assert that mobile phones connect to the nearest tower, which would place a suspect within a given radius of the tower. However, this assumption does not always hold, as certain towers can handle calls up to 20 miles away. According to the article, “Which tower a phone connect with depends on such factors as how thick the nearby foliage and walls are, the size of nearby cars and bodies of water, and how well the handset is working. None of this information is usually recorded.” Cell tower data is most often used in violent crime cases.
In light of the high error rate in the use of cell tower data, lawyers must not take the government’s assertion of the meaning of the data at face value. Instead, defense attorneys should retain experts to analyze the cell tower data and be prepared to undermine the prosecution’s conclusions from that data at trial.