An Opinion on Historical Cell Site Location Evidence (with an Peculiar Explanation of Rule 702)

In United States v. Medley, 312 F.Supp.3d 493 (D. Md. 2018), an FBI agent prepared charts "showing the geographic layout of the various cell towers to which [Jovon] Medley's phone supposedly connected at the time and date of [a] carjacking." United States District Judge Paul W. Grimm overruled Medley's objection to these charts and testimony about them, but he also directed the expert to limit his testimony so as to avoid "reliability" concerns. This limiting technique is becoming increasingly popular for forensic science testimony that clearly has some probative value but is not as "scientific" as one might hope. 1/

Citing an opinion from the Court of Appeals for the Seventh Circuit, Judge Grimm noted that "[c]uriously, despite the frequent admission of historical cell site location evidence by trial courts in criminal cases, '[n]o federal court of appeals has yet said authoritatively that historical cell-site analysis is admissible to prove the location of a cell phone user.'" He added that "the Circuit Courts that have considered admissibility of this evidence have split in their assessment of its reliability, and consequent admissibility." This split, as described in Medley, seems to emanate from an unpublished opinion of the Sixth Circuit in United States v. Reynolds, 626 Fed.Appx. 610, 614–15 (6th Cir. 2015),

The Reynolds court did not exclude testimony linking a cellphone to a location, for the government only used the cell tower records to rule out the presence of the phone in certain areas. But the Reynolds court was unimpressed with the argument that "historical cell site location analysis was reliable because it had been tested and accepted by the law enforcement community" and "that the methodology had been tested successfully over a thousand times in locating suspects with historical cell site tracking data." The court of appeals disdainfully wrote that:

This claim appears to be precisely the sort of “ipse dixit of the expert” testimony that should raise a gatekeeper's suspicion. While being successfully employed “1000 times” may sound impressive, the claim is not subject to independent peer review and fails to establish an error rate with which to assess reliability because there was no information on how many times the technique was employed unsuccessfully.

After a digression on whether or when cell site location evidence could be presented by a lay witness (Judge Grimm acknowledged the "impressive credentials and qualifications" of the witness to testify as an expert), the opinion equated Rule 702's "reliability" requirements to Rule 401's definition of relevance:

[T]he essence of Rule 702 is to avoid misleading the jury with unreliable evidence (which, by its very nature, is irrelevant, because unreliable evidence has no tendency to make a fact that is of consequence to the litigation more probable than it would be without the evidence, and irrelevant evidence fails to be helpful to a jury). Opinions that are solidly grounded in the facts of a particular case, employ reliable methodology or principles, have passed scrutiny by other experts in the same field, and which were reached by strict adherence to established standards and procedures are helpful. Those that are not amount to nothing more than scientific or technical guesses.

But reliability falls on a continuum. "Helpful" as used in Rule 702 is by not a simple corollary of the definition of relevance as the tendency to make a fact more probable. Expertise encompasses more than just two states--the very secure and the useless. Probative but imperfect information fills a middle range, and the relevance requirement (in Rules 401 and 402) does not bar evidence in this zone. "Guesses" by someone who is good at guessing are relevant--they alter the subjective probability of the contested fact. But even shrewd guesses may be excluded under Rule 702 if and when they are dressed up as scientific facts or impeccable wisdom. Moreover, Rule 403, which requires that prejudicial effect not substantially outweigh probative value, also supports such exclusion.

The end result in Medley can best be  understood in this light. The inferences from the cell tower data, Judge Grimm concluded, must be limited to "general location" and must include "a candid explanation of the accuracy of the particular location method used, which must, by necessity, include its limits as well as strengths." At that point, it becomes probative and helpful enough to satisfy rules 403 and 702.

Of course, how to explain "accuracy" when a "mathematical error rate has not been calculated" remains something of a puzzle, but Judge Grimm announced that

While I will allow the Government to elicit the opinion from SA [Special Agent] Fennern that the location of the defendant's cell phone was “consistent with” the location of the crime scene at the time of the carjacking, he may not do so until after he has fully explained during direct examination the inherent limitations of the accuracy of his location evidence—namely, the phone can only be placed in the general area of the cell tower sector that it connected to near the time of the carjacking, and that it cannot be placed any more specifically within that sector.

This approach reflects the judgment that more definite inferences from cell tower records would not be sufficiently reliable or that such testimony would not be worth the time it might take for a battle over the more powerful assertions. At the same time, the court deemed "general location" testimony with  disclaimers up front as sufficiently probative even if it provokes an extensive cross-examination. Indeed, the court slipped in the suggestion that the defense could use "learned treatises" in its cross-examination.

NOTE

1. In an unreported ruling from the bench in Medley, Judge Grimm also followed a middle path for firearms-toolmark testimony, limiting the examiner to "consistent with" testimony. See United States v. Johnson, No. (S5) 16 Cr. 281 (PGG), 2019 WL 1130258, at *20 (S.D.N.Y. Mar. 11, 2019) (declining to do the same; discussed at http://for-sci-law.blogspot.com/2019/03/another-us-district-court-finds.html).