Spring 2019 Gavel Spring Gavel 2019 - Page 21

Recent cases have shown that the government uses vague descriptions of cell site coverage areas. These usually consist of an arbitrary radius from the cell site in a circular pattern or in a directional or sectorized arc pattern. The prosecution’s expert witness stated that “a cell tower would generally have a coverage radius of about one to one-and-a-half miles.”4 He also said that urban areas could have smaller coverage areas, but he did not say how much smaller. Further, it was stated that cellular companies are installing small cells that may cover an area of 10 meters. As in the following cases, the radius is typically arbitrary and not scientifically determined. The prosecution will typically create a coverage area that is its “best case” and encompasses the crime scene, thus “proving” that the defendant was in the area of the crime scene. Hundreds of small cells could fit in a circle with a radius of one and a half miles. It is very clear that identifying the cellular coverage of a cell cannot be done arbitrarily. A much more scientific approach is needed. When the prosecution provides this type of map as evidence, it is important for the defense to obtain the CDR and CSLI information directly from the wireless operators and hire its own expert to create coverage plots that are based on a more scientific approach. People v. Brim 5 Case Analysis United States v. Carpenter 1 While all the press in this case is about Fourth Amendment rights, a cellular network design expert will investigate the actual testimony in regard to the determination of the cell site coverage area. In Carpenter, the U.S. Supreme Court held that police must usually get a warrant to access Figure 3: Cell site with 120 degree sector historical CSLI. and 2-mile radius At trial in Timothy Carpenter’s case, FBI agent Christopher Hess said that in an area like Detroit the cell sector’s signal could reach “typically anywhere from a half-mile to two miles.” 2 The government assumed a three-sector cell each with a 120-degree angle for each sector with a radius of two miles. The image would look something like Figure 3, with the arrow pointing to the proposed coverage area. This is not the exact location of the cell site in the case, but a sector with a two-mile radius is quite large, and in reality, there could be a dozen or more cells within this arc. Also, the actual coverage would look nothing like the arc shown in this figure. Thus, again it is clear that the government over estimates and simplifies the coverage area. By using a more scientific approach, the defense team can mitigate or even eliminate the prosecution’s argument about the phone being within the coverage area at the time of the crime.   United States v. Davis 3 The defendant in United States v. Davis was charged with committing several armed robberies. MetroPCS supplied 67 days of cell site records for the phone in question, as well as the relevant cell site locations. In Ronald Brim’s case, the prosecution’s expert used a one-mile radius for each cell site. This was the “outside reach” or best case for the prosecution. Los Angeles is very dense and nearly all of its cell sites are sectorized. Thus, this representation of the cell site coverage was Figure 4: Omnidirectional cell with highly slanted toward the arbitrary one-mile radius prosecution. In all these cases and many more, prosecutors used arbitrary methods of calculating the coverage of a cell site and used the “best case” scenario for them to place the phone at the crime scene. Daubert requires that “scientific methodology” be used. This is an opportunity for defense attorneys to contest the prosecution’s methods and to use an expert witness that will bring more proven methods of determining cell site coverage.   Expert Witness The defense team brings in an expert witness to analyze the mobile and network data, make a determination as to the location of the phone at the time of the incident, and dispute the prosecution’s claims concerning the location of the mobile phone. This must be based on scientific evidence that satisfies the Daubert6 or Frye7 rules depending on the jurisdiction in which the case arises. To meet the Frye standard, scientific evidence presented to the court must be interpreted by the court as "generally accepted" by a meaningful segment of the associated scientific community. The Daubert standard supersedes Frye and provides a set of guidelines to assure that data is relevant and comes from “scientific knowledge.” The data must be presented by an expert witness complying with Rule 702, which is as follows: A witness who is qualified as an expert by knowledge, skill, experience, training, or education may testify in the form of an opinion or otherwise if: (a) the expert’s scientific, technical, or other specialized knowledge will help the trier of fact to understand the evidence or to determine a fact in issue; SPRING 2019 21