They were two bank robbers who never would have been caught ten years ago. But last year, they were tracked, followed, and convicted by federal agents who did nothing more than get a court order for "cell tower dumps." It's a win for crime fighting, but is the price of surveillance too great?
Over at Ars Technica, Nate Anderson has a great story about the kinds of information law enforcement can get about your life just from mobile provider data — and with very little court oversight.
A pair of bank robbers in the American southwest were targeting rural banks for months, picking up $3,000 here and $6,000 there. They always wore masks, so they couldn't be identified from surveillance footage. And they struck in places that were remote enough that law enforcement couldn't arrive soon enough to give chase. But one witness noticed a guy hanging around one of the banks before the robbery talking on his cell phone. And that gave the FBI an idea.
Why not requisition the records of everyone who'd made calls near cell phone towers close to the banks, to see if there were any common numbers that popped up right before the robberies? To get that data, known as a cell tower dump, they didn't even need a warrant. They focused in on the most rural banks, so that they'd get the sparsest data. Still, they wound up with hundreds of thousands of numbers to pore over.
Once they'd found two numbers that matched their criteria, the FBI were able to reconstruct the thieves' movements better than if they'd actually been tailing the men. That's because your cell phone's number is logged by every cell tower you pass — this is what keeps your phone on the network at all times (ideally), but it's also what makes your phone the ultimate tracking device.
Here's what the FBI discovered, just by tracking which cell towers the thieves were near:
On 11/25/2009, both CAPITO's and GLORE's mobile telephones begin the day at 6:31AM on the same cell tower in Show Low, Arizona, when CAPITO calls GLORE's mobile telephone. Both mobile telephones remain in Show Low until CAPITO's telephone uses a cell tower near Punkin Center, approximately 30 miles south of Payson, Arizona. By approximately 11:00AM, both CAPITO's and GLORE's phones are using the same cell tower in Star Valley, Arizona, approximately 5 miles east of Payson, Arizona, and likely covering areas of Payson, Arizona. By 11:50AM, both CAPITO's and GLORE's mobile telephones are using towers in Payson, Arizona, that are almost certainly within the coverage area of the Compass Bank located at 613 S. Beeline Highway, Payson, Arizona. GLORE's telephone remains on these Payson cell towers and last uses a Payson cell tower located only 1 mile from the Compass Bank at 3:27PM when he receives a call from CAPITO's cell telephone.
CAPITO's telephone continues to use the Star Valley and Payson towers through the 3:27PM call, when CAPITO's telephone is using a cell tower located only 1.7 miles from the Compass Bank. At approximately 3:29PM, the High Country Bandits rob the Compass Bank, 613 S. Beeline Highway, Payson, Arizona. The next call on either GLORE or CAPITO's mobile telephones is at approximately 4:40PM when they are contacting each other and both are using the cell tower near Punkin Center, approximately 30 miles south of Payson, Arizona. Both mobile telephones remain using that cell tower throughout the night and return to Show Low, Arizona by 11:00AM the next day.
The question is, should those hundreds of thousands of other people's numbers — and their movements — be exposed to FBI scrutiny in the process of catching a couple of two-bit crooks? And how comfortable are you knowing that a simple court order allows a law enforcement agency to get this intimate with your daily movements?
Read more at Ars Technica