Cell Site Evidence is Junk Science (and a Recent DC Opinion Could Help Keep It Out of Court)

March 10, 2020

Smart city and communication network concept. abstract mixed media.By Sara Kropf

Since I handle only white-collar criminal matters, I don’t deal with forensic science as often as other criminal defense lawyers do. I’ve never had a case turn on DNA samples or bitemark evidence or analysis of clothing fibers. This post is a bit of a frolic and detour, but, hey, it’s my blog and I’ll do what I want.

A few years ago, I was appointed to represent a defendant in an appeal that dealt with cell site evidence. I was troubled by the supposed “science” behind it, and we raised an issue as to its admissibility on appeal. (The case is still pending.)

An excellent  decision from a trial court judge in the District of Columbia could be used to raise questions about this type of evidence. (H/t to Randy Balko who wrote about the decision in the Washington Post.)

Trying to exclude “junk science” is a critical part of being a defense lawyer, but it’s an uphill battle. Even after a crucial 2016 report about the prevalence of junk science in court, judges still regularly–and somewhat blindly–admit it.

If you aren’t familiar with it, historical cell site evidence is evidence that allegedly shows the location of a cell phone based on identification of the  location of a cell tower off which a defendant’s cell phone “pinged” at a specific time.

Here’s how it works: The government will subpoena “call detail records” from a cellular network provider. Those records show the date, time, and phone numbers of calls or texts. They also show the cell site location information or cell tower information from which the call or text was made.

The government expert uses that information to pinpoint the location of a defendant (or witness or victim) at a particular date and time. The expert may also testify about the defendant’s movement over time—i.e., the defendant moved from this location to another location in a particular time frame.

[NB: This is different from live GPS tracking. A phone can be tracked in real time, using its GPS capabilities–and can pinpoint a location within 5-10 feet. But that is different from historical cell site analysis, which is looking back in time based on call detail records.]

As you can imagine, this is powerful evidence at trial. Imagine a murder case where the defendant’s alibi witness testifies that the defendant was in his house the whole time—a house that is a quarter mile from the scene of the crime. The FBI expert testifies that his phone was not pinging off the cell tower closest to this house but rather the cell tower closest to the scene of the crime.

Pretty compelling, right? Yes, right up until you dig into the details.

These conclusions depend on the factual assumption that the cell phone is pinging off the closest cell tower. But that’s not always the case.

A cell tower in a crowded area may be too busy to handle a call or text message. A phone will automatically find the closet available cell tower to use. The next closest one may also be too busy to handle the signal. The phone will keep looking for a site that can handle the signal. And that cell tower could be a bit of a distance away.

As a result, even though the call detail record shows that a phone pinged off the cell site at Fourth Street and Massachusetts Avenue at 1 pm on March 16, 2018, the phone could have been many blocks away from there because the cell site closest to the phone’s physical location was too busy to transmit the call.

Cell site evidence can, of course, show that someone was in Washington, DC and not its far-flung suburbs or New York at a specific time. But to use it to pinpoint an exact location is highly questionable.

Unfortunately, that hasn’t stopped court after court from allowing this “expert” testimony into evidence. The complete lack of peer-reviewed scientific studies also hasn’t kept it out of court.

A trial court judge here in DC recently issued an opinion on a different kind of junk science and the reasoning could be used to challenge cell site evidence. Judge Todd Edelman (a well-regarded judge ) issued an opinion in United States v. Tibbs excluding much of the government expert’s proposed testimony about firearm and toolmark identification evidence from trial.

Here’s the link to the Tibbs opinion.

Judge Edelman evaluated whether toolmark identification evidence was admissible under Daubert and the D.C. Court of Appeals’ decision in Motorola. Toolmark identification is when an expert testifies that a particular firearm was the source of a particular firearm cartridge through an examination of the markings on the cartridge casing.

It’s a lengthy opinion and I won’t go into all the details. A few relevant points:

One. The trial court got into the weeds. There were reports and experts and “lengthy arguments by skilled and experienced counsel” that lasted several days.

Two. The court summarized its primary reasons for restricting the government’s use of this evidence as

the inability of the published studies in the field to establish an error rate, the absence of an objective standard for identification, and the lack of acceptance of the discipline’s foundational validity outside of the community of firearms and toolmark examiners.

  • Cell site evidence doesn’t have any published studies with an error rate, there is no objective standard to determine how far away someone is from a tower, and the only foundational validity appears to be for experts who testify for the government.

Three. The court did not entirely exclude the expert. The expert could testify that the recovered firearm could not be excluded as the source of the recovered cartridge casing. In other words, he could say “that the firearm may have fired the recovered casing,” emphasis in original, but “may not state an ultimate conclusion in stronger terms.” The expert  could not testify that individual marks are unique to a particular firearm or that a cartridge could be matched to a particular firearm.

  •  Cell cite evidence could likely be appropriately used to pinpoint a general location for someone—in a particular city or even perhaps area of a city. But it shouldn’t be used to pinpoint an exact location as an “expert” opinion.

Four. The court (politely) noted that existing case law allowing this evidence has “limited persuasive value” because the courts allowing this testimony “have not engaged in a particularly extensive or probing analysis of the evidence’s reliability.”

Yet, the case law in this area follows a pattern in which holdings supported by limited analysis are nonetheless subsequently deferred to by one court after another. This pattern creates the appearance of an avalanche of authority; on closer examination, however, these precedents ultimately stand on a fairly flimsy foundation. The NRC credited Professor David Faigman—one of the defense experts who testified at the Daubert hearing in this matter—with the observation that trial courts defer to expert witnesses; appellate courts then defer to the trial courts; and subsequent courts then defer to the earlier decisions.

  • This is precisely what happens in cell site cases. There are multitudes of decisions allowing it, none of which analyze its reliability to the extent Judge Edelman does, yet the sheer number of decisions admitting this evidence gives a trial court judge plenty of “cover” to do the same.

Five, the court addressed the fact that the “scientific community” in which toolmark identification was “generally accepted” was not a scientific community at all. It’s the people who make money off testifying to this stuff.

If Daubert, Motorola, and Rule 702 are to have any meaning at all, courts must not confine the relevant scientific community to the specific group of practitioners dedicated to the validity of the theory—in other words, to those whose professional standing and financial livelihoods depend on the challenged discipline.

  • While FBI agents are not the same as paid experts, they certainly have a similar financial incentive. If the evidence is not reliable, then that (highly valued) part of their jobs will disappear. Plus, the FBI helps investigate cases and assists the prosecution in meeting its burden of proof. That’s not an unbiased “scientific” community at all.

Six. The court rejected the government’s argument that cross-examination of the expert will cure the problem. This is always the fallback for a trial court judge: the defense can vigorously cross-examine the expert to show why the opinion is not reliable. But the issues for toolmark identification “seem far too complex for a series of questions on cross-examination to allow a full understanding of the limitations of the field.” It would be “fanciful” to think that a “lay jury could adequately understand these issues” and “unrealistic” to think that an “average attorney in the average trial” could raise these issues.

  • Cell site evidence may be a bit simpler to explain, but that doesn’t mean that the average lawyer in the average case can adequately challenge it. Plus, leaving it to defense lawyers–unassisted by the FBI–is a complete abdication of a court’s role under Daubert.

Worth a Shot

I’m not saying this decision will prevent the admission of cell site evidence. For starters, the government didn’t appeal it, so it’s only a trial court decision. (The government obviously feared making it the law of the land in DC but I’m sure other judges on the trial court here know about the decision.)

But, it’s worth a shot—whether you are in DC or not, this is a good example of how a judge should analyze forensic science to make sure it’s not junk.

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