Serial, Cell Site Location Information, and Experts . . . on a Wednesday

It’s not Thursday, but I’m going to throw it back a few years to 2014. Like the rest of the nerds I know, I became obsessed that year with the podcast Serial. The first season of that podcast chronicled the prosecution of Adnan Syed for the 1999 murder of his ex-girlfriend, Hae Min Lee. Host Sarah Koenig meticulously sifted through the evidence and conducted goodness-knows-how-many interviews with everyone connected to the case, including numerous recorded interviews with Syed, who is serving a life sentence in a Maryland prison. Syed claims that he did not kill Lee, whose body was discovered six weeks after she disappeared buried in a Baltimore park. Koenig spends the first several episodes of the podcast describing inconsistencies in witness’s accounts of the day Lee disappeared—inconsistencies that raise doubts about Syed’s guilt. But in episode five, Koenig, with the help of her producer, analyzes the evidence that the State offered regarding which cell towers serviced calls to Syed’s phone during the time that one of Syed’s friends claimed Syed was burying Lee’s body. The producer concludes:

“I think they were probably in [the park] . . .   Because . . . the amount of luck that you would have to have to make up a story like that and then have the cell phone records corroborate those key points, I just don’t think that that’s possible.”


This portion of the podcast factored significantly in my assessment of the State’s case against Syed. It also illustrates more broadly just how probative cell site location information can be. Unlike friends and eye-witnesses, cell towers don’t have motives, bad memories, or shifting stories. The location information they provide is not always exact—but it is unbiased and constant. While cell tower location evidence was relatively new at the time of Syed’s trial in 2000, it has since become a far more routine part of criminal prosecutions.

Increasing demand for location information. One of the nation’s largest cellular service providers, AT&T, reported that in the first half of 2017, it received 36,133 criminal and civil demands for historic location information. This was an increase of more than 2,500 from the previous six months. While it is clear that this kind of information is frequently used to investigate crime, it is less clear what standards must be satisfied for it to be admitted at trial. Must testimony about cell site location information be provided by an expert or can an informed lay witness use cell phone records to create a roadmap of the defendant’s whereabouts for the jury?

The subject of the testimony. Law enforcement officers who have reviewed cell phone records in the course of an investigation often testify about what they have gleaned from those records. Such testimony frequently is accompanied by an exhibit that summarizes the information gleaned from those records, such as a map that displays the location of the cell towers with which a particular phone made contact, significant locations in the case, and excerpts from the phone’s call log.

To establish the relevancy of this information, a witness generally must testify about the interplay of cell phones and cell phone towers. That testimony might go something like this:  Cell phones operate as two-way radios, transmitting and receiving signals through cell towers in a cellular network. Cell towers contain multiple antennas that are positioned to cover certain geographic areas or sectors. When a cell phone is used to make a call, send a text message, or connect to the internet, the phone connects to the cell tower sector with the strongest signal. This is typically, but not always, the closest tower. As the cell phone user moves around, the cell phone automatically switches to any other tower sector emitting a stronger signal. Cell phone providers create and maintain records of cell phone interaction with cell phone tower sectors for purposes of optimizing service and accurately billing customers. By examining those records, a person can determine the general location of a cell phone at the time it connects to a tower. See State v. Johnson, 797 S.E.2d 557 (W. Va. 2017) (recounting this explanation of cellular technology).

The line between expert and lay opinion. Several courts have determined that testimony based on historical cell site data that goes beyond conveying the cellular records to the jury requires that the witness be qualified as an expert. See, e.g., United States v. Evans, 892 F. Supp.2d 949, 953-54 (N.D. Ill. 2012); Wilder v. State, 991 A.2d 172, 199-200 (Md. App. 2010); Collins v. State, 172 So.3d 724, 743 (Miss. 2015). The Supreme Court of Mississippi explained in Collins, for example, that a lay witness may testify about the information in a cell phone record and may inform the jury about the location of cell phone towers. The court distinguished this type of testimony from that which purports to pinpoint the area in which the cell phone user was located based on cellular data, stating that the latter type of statements are based on scientific, technical, or other specialized knowledge that is the proper subject of expert testimony. The Collins court explained that the expertise necessary would not be so great as that required of a medical doctor, but that “some specialized knowledge beyond that of the average, randomly selected adult is required to analyze cellular phone records and other data to determine the location, general or specific, of a certain cell phone.” Id. at 744.

One commentator has opined that cellular records should only be admitted through expert testimony for two reasons:  (1) the technology is specialized, scientific and technical; (2) lay witnesses are without sufficient information for the defense to cross-examine. Alexandra Wells, Ping! The Admissibility of Cellular Records to Track Criminal Defendants, 33 St. Louis U. Pub. L. Rev. 487, 516 (2014). Some courts have adopted bright-line rules requiring that a witness be qualified as an expert to present evidence of historical cell site data.  See United States v. Banks, 93 F. Supp. 3d 1237, 1248-49 (D. Kan. 2015); Johnson, 797 S.E.2d at 566.

Not all courts are buying. The Supreme Court of Missouri sitting en banc held in State v. Blurton, 484 S.W.32d 758 (Mo. 2016), that a law enforcement officer who mapped the location of each cell tower to which the defendant’s cell phone connected around the time of the murders and testified, based on the map, about the defendant’s direction of travel on a specified highway during the time in question did not have to be qualified as an expert.  The court distinguished cases in which a lay witness had improperly attempted to pinpoint a defendant’s exact location within a small geographic area, stating that “[e]ven if Mr. Blurton’s cell phone connected to a cell tower 30 miles away from his actual location at the time of each call, the witness could still reasonably infer Mr. Blurton’s general path of travel from Garnett to Cole Camp without using specialized skill or knowledge.” Id. at 772.

What’s the rule in NC?  North Carolina’s appellate courts have not yet considered whether locational information based on cell phone records is the proper subject of lay or expert testimony.  The court of appeals has, however, approved testimony by lay witnesses on related subjects. In State v. Jackson, 229 N.C. App. 644 (2013), the court held that the trial court did not err by permitting a law enforcement officer, who was not qualified as an expert, to testify about the defendant’s location based on tracking by an electronic monitoring device worn by the defendant. The court described the testimony as rationally based on the officer’s perception of the tracking data, not the law enforcement officer’s personal knowledge of the defendant’s location. And, in yesterday’s unpublished decision in State v. Clark, No. COA16-1194, 2017 WL 4126974, __ S.E.2d ___  (N.C. App. 2017) (unpublished), the court of appeals determined that the trial court did not err by allowing lay witnesses to testify that they tracked the defendant’s location by using the Find my iPhone app and searching for the victim’s stolen phone. The defendant argued that the admissibility of the iPhone application evidence was contingent upon testimony establishing its reliability. The court rejected that argument, characterizing the testimony from the witnesses as akin to that in Jackson because they described “their personal perceptions after observing tracking data,” namely the blue dot that represented the victim’s phone.

The absence of an appellate case does not mean, of course, that locational testimony based on cell records is not being used in North Carolina criminal trials. It is. See State v. Perry, 776 S.E.2d 528, 534 (N.C. App. 2015) (holding that State’s obtaining of cellular records first acquired by the cellular company was not a Fourth Amendment search); State v. Hurtado, No. COA15-211, 2015 WL 8741007, 781 S.E.2d 351 (N.C. App. 2015) (unpublished) (same); State v. Smith, No. COA15-614, 2016 WL 1743699, 786 S.E.2d 434 (N.C. App. 2016) (unpublished) (noting admission of law enforcement officer’s testimony about the location of defendant’s cell phone based on his analysis of phone records); State v. Nolasco, No. COA15-972, 2016 WL 1566320, __ S.E.2d ___ (N.C. App. 2016) (unpublished) (noting admission of evidence that defendant’s phone connected forty-seven times to the cell tower that serviced the area encompassing the murder site).

Litigators, please share your experiences. Is location evidence based on cell site data becoming common in your neck of the woods? Are trial judges requiring that such testimony be given by a qualified expert?

Nerds like me would love to know. And check out Season Two of Serial.  It’s awesome.

Author’s Note: Thanks to my colleague, Jeff Welty, the School’s resident expert on cell phone tracking, for research and analysis that contributed to this post. 

2 thoughts on “Serial, Cell Site Location Information, and Experts . . . on a Wednesday”

  1. At trial, the State called an FBI Special Agent who testified as to defendant’s whereabouts on 18 October 2007, which were pinpointed by over 100 cellular phone calls. Defendant consistently utilized cellular phone towers in the Raleigh-Durham area in the morning and early afternoon, towers in the Durham area in the late afternoon, and between 4:00 p.m. and 7:00 p.m., towers indicating a progression westbound. Beginning at 7:23 p.m., defendant utilized one of the three cellular towers in the Wilkesboro area, thus placing him in the vicinity of the victim’s home and scene of the murder. Defendant made a four-second call to the victim’s work phone at 7:23 p.m. through a Wilkesboro tower. Following that call was a 12-minute gap. Beginning again at 7:35 p.m. and through 7:46 p.m. defendant made a series of calls to his wife, family members, and a friend, first utilizing towers in the Wilkesboro area, then towers indicating a progression east. Beginning at 7:46 p.m. and through 7:55 p.m., defendant used towers crossing the Wilkes County line. Defendant made 22 subsequent calls from 8:00 p.m. to 11:00 p.m. which indicated defendant was progressing eastward through Winston-Salem, Greensboro, and finally to Durham. See State v. Miles, 222 N.C. App. 593, 598 (2012).


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