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New Jersey Supreme Court Excludes CSLI Testimony Based on Agent’s ‘Rule Of Thumb’ Method for Determining Defendant’s Location

by Anthony W. Accurso

The Supreme Court of New Jersey held a lower court erred when it allowed an FBI agent to testify about cell site location information (“CSLI”) regarding defendant’s alleged location during the timeframe the charged offense occurred based on the agent’s personal “rule of thumb” approximation of cell tower ranges in the area, which was solely based on the agent’s personal observations and “training and experience” rather than any actual data collected from the towers in question.

On December 25, 2015, Rosette Martinez was with her daughter, Samantha, and Samantha’s friend. A man came to the home, claiming to be a repair contractor sent by a friend of the family. Once inside, he pulled out “a long gun,” forced the women to the ground, bound them, and “stole jewelry, two Amazon Kindles, and credit cards.”

Within days, police developed a working theory that Roberson Burney—the brother of Mark Burney, a contractor who had done work in the victim’s home—was the robber. Bloomfield Police arrested him on December 29.

On April 28, 2016, a grand jury charged Burney with first-degree robbery, second-degree burglary, fourth-degree aggravated assault, third-degree criminal restraint, third-degree unlawful possession of a weapon, second-degree unlawful possession of a weapon for an unlawful purpose, third-degree burglary, and third-degree theft.

Among the issues raised prior to trial, Burney objected to proposed testimony by Special Agent Ajit David, a member of the FBI’s Cellular Analysis Survey Team. David intended to testify that it was his “rule of thumb” determination based on his personal observations that the coverage area of nearby cell towers was approximately one mile. Since the victim’s home was just inside this area for a tower “pinged” by Burney’s phone during the robbery, David’s testimony essentially established Burney’s presence in the vicinity of the crime scene. On July 6, the Court held a hearing pursuant to Frye v. United States, 293 F. 1013 (D.C. Cir. 1923), to determine the admissibility of David’s testimony as an expert.

During the hearing, David explained that cellular towers have three overlapping zones of coverage that, when visualized as cones on a map, illustrate the area where a cell phone could be located when it pings a tower, since the phone company keeps records of which tower and zone is in use by the cell phone in question. The issue was how far out each cone extended. David claimed the cone “had an approximate length of one mile.” He based this on his “training and experience” and the inference that Sprint deployed each tower that far apart to “avoid coverage gaps.”

The Court observed that David “further noted that a tower’s range and coverage area can be affected by many factors, including the height of the antenna, surrounding terrain and buildings, signal frequency, transmitter and phone power ratings, and antenna direction, but he did not offer measurements or data as to those specific factors when testifying as to as estimated range for [the tower pinged by Burney’s phone].”

Additionally, the Court noted that David failed to measure the “actual coverage area” through “drive testing” or “propagation maps.” Nevertheless, the trial court allowed David’s testimony, and Burney was subsequently convicted on all charges except for third-degree unlawful possession of a weapon. He was classified as a persistent offender and sentenced to life without parole.

Burney timely appealed, claiming, among other things, that David’s testimony was admitted in error. The Appellate Division granted one of his claims, but Burney appealed to the state Supreme Court over the denied claims, including the claim arising from David’s testimony.

The New Jersey Supreme Court noted that, “[a]cross the nation, state and federal courts have accepted expert testimony about cell site analysis for the purpose of placing a cell phone within a ‘general area’ at a particular time.” See United States v. Hill, 818 F.3d 289 (7th Cir. 2016).

The Seventh Circuit in Hill, concerned that a “jury may overestimate the quality of the information provided by” cell site analysis, admonished that the “admission of historical cell site evidence that overpromises on the technique’s precision—or fails to account adequately for its potential flaws—may well be an abuse of discretion.”

In Hill, the testifying expert used cell site information to track the defendant’s whereabouts during a two-day period, with the implication that the defendant’s phone was located in the general area of a credit union the day it was robbed. The agent had no knowledge of the particular characteristics of the cell tower in question and did not testify about the tower’s specific range. During the agent’s testimony, he stressed that the use of the defendant’s cell phone’s use of the cell tower “did not mean that [the defendant] was right at that tower or at any particular spot near that tower.” According to the Hill Court, that disclaimer saved the agent’s testimony that the defendant’s phone was in the general area of the tower.

The Court then discussed the “net opinion” rule, a corollary of N.J.R.E. 703, which “forbids the admission into evidence of an expert’s conclusions that are not supported by factual evidence or other data.” Townsend v. Pierre, 110 A.3d 52 (N.J. 2015). “The rule requires that an expert ‘give the why and wherefore’ that supports the opinion, ‘rather than a mere conclusion.’” Id. When experts base their testimony on personal views, “rather than objective facts,” such unsupported views must be excluded from evidence under the net opinion rule, the Court stated. Pomerantz Paper Corp. v. New Cmty. Corp., 25 A.3d 221 (N.J. 2011).

The Court, discussing David’s “rule of thumb” approximation regarding tower coverage, wrote: “[he] did not testify that such approximation is common practice in cell tower analysis, or that his one-mile ‘rule of thumb’ had been used by any other agent or radio frequency engineer. Additionally, [he] admitted that he did not review the height of the [tower], did not review its rated power, did not calculate the estimated absorption of radio energy by nearby buildings or hills, did not review the specific angle of the tower’s antenna, and did not review any diagnostic data from the tower on December 25.”

The Court compared David’s testimony with that of the agent in Hill, who provided the disclaimer during his testimony that the fact the defendant’s cell phone pinged a specific tower did not mean that the defendant was right at or near the tower. In stark contrast, David provided no such disclaim; in fact, he testified that based on his “rule of thumb” conclusion, it was “highly, highly unlike[ly]” the victim’s home could fall outside the coverage area for the tower in question.

Ultimately, the Court concluded this case is indistinguishable from United States v. Evans, 892 F. Supp. 2d 949 (N.D. Ill. 2012), where the federal district court “held that the testifying expert’s estimates of the ranges of different cell towers were unreliable because they were based solely on the experts training and experience.” The Evans Court declared that approximately the coverage range of cell site towers requires more than just “training and experience.” It also requires “scientific calculations that take into account factors that can affect coverage.” Id.

Turning to the present case, in light of the lack of supporting data for David’s estimation of the cell tower’s coverage area, the Court concluded that his testimony failed to account adequately for the potential flaws in his “rule of thumb” opinion. Thus, the Court ruled his “rule of thumb” testimony constitutes an improper net opinion because it was not supported by any factual evidence or data.

Accordingly, the Court ordered Burney’s conviction reversed and remanded for a new trial. See: State v Burney, 298 A.3d 1080 (N.J. 2023).  

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