We've frequently talked about law enforcement and the intelligence community accessing and making use of cell site location data, which looks to figure out where people are based on what cell towers they're connected to. Law enforcement likes to claim that it doesn't need
a warrant for such data, while the NSA has tested a pilot program
recording all such data, and says it has the legal authority
to collect it, even if it's not currently doing so.
However, as anyone with even a basic geometry education recognizes, which cell tower you're connected to does not give you a particularly exact location. It can be useful in putting someone in a specific (wide) area -- or, much more useful in detailing where someone is traveling over long distances as they repeatedly switch
towers in a particular direction. But a single reading does not give you particularly exact location details. I had naturally assumed that most people understood this -- including law enforcement, lawyers, prosecutors and judges -- but it turns out they do not. A rather depressing story in The Economist notes that, thanks to this kind of ignorance (combined with bogus cop shows on TV that pretend cell site data is good for pinpointing locations), cell site location data is frequently used to convict innocent people
. The story opens with a ridiculous example, in which a woman was pressured into a plea bargain based on totally false claims about tower location data:
SOMEONE strangled a prostitute in Portland, Oregon in 2002. The police arrested Lisa Roberts, the victim’s ex-lover, who spent more than two years in custody awaiting trial. Shortly before the trial the prosecutor told Ms Roberts, via her lawyer, that tower data collected by Verizon, her mobile-telephone network, showed precisely where she was at the time of the murder. As her lawyer recalled, the prosecutor said Ms Roberts could be “pinpointed” in a park shortly before the victim’s naked and sexually assaulted corpse was found there. She was told she faced 25 years to life in prison. She accepted a deal to plead guilty and serve 15 years.
But the high-tech evidence against her was bunk. Routinely collected tower data can place a mobile phone in a broad area, but it cannot “pinpoint” it. That would require a special three-tower “triangulation”, which cannot reveal past locations. It took a decade for Ms Roberts’s guilty plea to be thrown out. On May 28th she left prison, her criminal record clean, after nearly 12 years in custody.
Obviously, things like GPS do
allow for much more precise targeting of location (which may be why the NSA is focusing on that
instead of cell site location data), but too many people confuse cell site location data with GPS. What's ridiculous is that this mistake isn't just being made by random people -- but prosecutors and lawyers responsible for criminal cases that can destroy an innocent person's life.
This really points to a larger issue: people have this tendency to believe that technology can answer all questions. The NSA's fetishism of surveillance via technology is an example of this. There's data
there, so it becomes all too tempting to assume that the data must answer any possible question (thus, the desire to collect so much of it). But the data and the interpretations it can lead to are often misleading or simply wrong. And that's especially true when dealing with newer technologies or forms of data collection. That the criminal justice system could go decades without everyone
recognizing the basic geometric limits of cell site location data based on a single cell is... both astounding and depressing. But it's also a reminder that we shouldn't assume that just because some evidence comes from some new-fangled data source it's automatically legitimate and accurate.