Judge Joan H. Lefkow of the United States District Court in the Northern District of Illinois – Eastern Division has ruled in United States v. Antonio Evans that a prosecution expert witness cannot testify about “granulization,” a method used to track someone via his or her cell phone location. The Honorable Joan Lefkow ruled that the witness is allowed to testify about other aspects of cell phone records and cell towers, but not specifically about granulization.
Special Agent Joseph Raschke testified for the prosecution about granulization, among other things. Granulization is a method by which an expert in cell phone tracing maps out the area that individual cell towers cover in a given region. Then, by examining which tower(s) a cell phone connected to, the expert can determine with a high level of accuracy an area where the cell phone user was likely to be at the time of the call. Raschke and other experts in this field base their conclusions as to where a person was on the assumption that a cell phone will automatically connect to the closest tower. However, as the defense’s expert witness points out, there are a multitude of factors that affect which tower a cell phone connects to, including tall buildings and a busy network.
For expert testimony regarding a particular method or theory to be admissible, it must pass the test created in Daubert v. Merrell Dow Pharmaceuticals, Inc. (1993). To pass the Daubert test, a court must consider and reconcile:
- whether the theory is based on scientific or other specialized knowledge that has been or can be tested;
- whether the theory has been subjected to peer review;
- the known or potential rate of error and the existence of standards controlling the theory’s operation; and
- the extent to which the theory is generally accepted in the relevant community.
Daubert, 509 U.S. at 593-94.
Besides the fact that granulization is inherently based on substantial assumptions (in that it takes for granted that the tower that was used was the closest tower), another flaw is that it has not stood up to the rigor of the scientific community. The fact is, granulization is a method that is used almost exclusively in the field of law enforcement; it has little to no validity outside the realm of catching criminals. As such, the validity and accuracy of the method can only be guaranteed by the expert witness himself, and cannot be corroborated by independent, outside sources. Although Raschke purports to have a 100% success rate, the method has not stood up to the scrutiny of the scientific community. For the foregoing reasons, granulization has not passed the Daubert test, and is not admissible as expert testimony.
The Honorable Joan Lefkow still allowed Special Agent Raschke to testify about cell towers and cell phones in general, but did not permit testimony about granulization. As such, this decision should be referenced if the prosecution is attempting to use cell tower data as evidence in proving where someone was. Until the scientific community accepts granulization, testimony on this issue may well be barred if the defense objects.
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