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United States v. Hahn

United States District Court, D. Hawaii

March 18, 2019

DEREK HAHN (3), Defendant.


          J. Michael Seabright Chief United States District Judge

         Defendant Derek Hanh (“Hahn”) seeks an order in limine excluding FBI Supervisory Special Agent Edwin Nam (“Nam”) from testifying as an expert witness regarding historical cell-site data pursuant to Federal Rule of Criminal Procedure 16 and Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579 (1993) (“Daubert I”). On March 13, 2019, the court held an evidentiary hearing, with Nam as the sole witness. For the following reasons, the motion is DENIED.

         I. BACKGROUND

         During the government's investigation, a warrant was issued to Sprint Communications for Hahn's cellular telephone records. Both parties agree that the Sprint records captured the phone's voice calls and text messaging transactional data, including the particular cellular tower that the phone accessed when voice calls and/or text messages were sent or received. It is also undisputed that the towers at issue in this case used approximate 120-degree sectors (sometimes called “faces”) to provide 360 degrees of coverage per tower. The Sprint records capture not only the tower used, but also the particular sector that connected at a particular time.

         Nam, [1] a supervisor at the FBI's cellular analysis survey team, testified that for each voice call or text message sent or received, the phone selects the tower that provides the best signal at that time.[2] The best signal, in turn, is determined by signal strength and signal quality. Nam was likewise clear that a cell phone does not always or necessarily utilize the nearest tower; instead it assesses its environment and uses the tower with the best signal. For example, he explained that in a perfectly flat area with no obstructions, the tower with the best signal would be the nearest to the cell phone. But various factors can impact which tower offers the best signal, including obstructions and topography.

         Based on this explanation, Nam testified that once he has identified a specific Sprint tower and its sector that was used on a specific date and time, he cannot conclude specifically where the phone was located, but can testify that it was used within the coverage area of that specific tower's sector. Finally, he explained that the coverage area for each tower is unique, and that he did not measure the coverage area for each tower identified in this case.

         II. ANALYSIS

         A. Federal Rule of Criminal Procedure 16

         Hahn first contends that the government failed to comply with its discovery requirements under Federal Rule of Criminal Procedure 16 (“Rule 16”). The court disagrees.

         Rule 16 requires the government to provide the defense with “a written summary” of the testimony it expects to adduce from an expert witness and that summary must “describe the witness's opinions, the bases and reasons for those opinions, and the witness's qualifications.” Rule 16(a)(1)(G). If the government fails to comply, the court has several options - permit discovery; grant a continuance; “prohibit that party from introducing the undisclosed evidence;” or “enter any other order that is just under the circumstances.” Rule 16(d)(2).

         The government complied with Rule 16. Its February 9, 2019 disclosure contained Nam's curriculum vitae, a separate written summary of Nam's qualifications, Nam's opinions, and an explanation of how he reached his opinions. ECF No. 382-2. Specifically, the government disclosed that Nam obtained the cell phone records for Hahn's telephone, and those records documented the cell towers and cell sectors that serviced that phone. Nam explained that mapping software was used using the latitude/longitude of the cell tower coordinates provided by the service provider, and the “cell sites associated with the target cell phone were located using the mapping software and the plotted cell site data.” Id. at PageID #8 of 15. Nam also explained that “the call detail records and a list of cell site locations were analyzed to illustrate an approximate location of the target cell phone when it initiated contact with the network.” Id. Finally, the government's disclosure included several historical cell site analysis maps. No. further disclosure was required.[3]

         B. Federal Rule of Evidence 702

          Next, Hahn seeks to exclude Nam's expert testimony ...

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