Digital privacyAn armed robber’s Supreme Court case could affect all Americans’ digital privacy for decades to come

By H. V. Jagadish

Published 30 November 2017

A man named Timothy Carpenter planned and participated in several armed robberies at Radio Shack and T-Mobile stores in Michigan and Ohio between 2010 and 2012. He was caught, convicted and sentenced to 116 years in federal prison. His appeal, which was heard by the U.S. Supreme Court on 29 November, will shape the life of every American for years to come – no matter which way it’s decided. The FBI found Timothy Carpenter because one of his accomplices told them about him. I believe the FBI could have obtained a search warrant to track Carpenter, if agents had applied for one. Instead, federal agents got cellphone location data not just for Carpenter, but for fifteen other people, most of whom were not charged with any crime. One of them could be you, and you’d likely never know it. The more people rely on external devices whose basic functions record and transmit important data about their lives, the more critical it becomes for everyone to have real protection for their private data stored on and communicated by these devices.

A man named Timothy Carpenter planned and participated in several armed robberies at Radio Shack and T-Mobile stores in Michigan and Ohio between 2010 and 2012. He was caught, convicted and sentenced to 116 years in federal prison. His appeal, which was heard by the U.S. Supreme Court on 29 November, will shape the life of every American for years to come – no matter which way it’s decided.

During its investigation of the robberies, the FBI got records not only of the phone calls made and received by Carpenter’s cellphone, but also its location over 127 days. The information clearly placed Carpenter’s phone nearby at the times and places of each of the robberies, providing strong circumstantial evidence against him. But it also revealed other information unrelated to the investigation, such as which nights Carpenter slept at home and what church he prayed in on Sunday mornings. The FBI didn’t get a search warrant for that information; the agency just asked Carpenter’s cell service provider, MetroPCS, for the data.

Carpenter is appealing his conviction on the grounds that his Fourth Amendment right to be protected from an unreasonable search was violated because his cellphone location was tracked without a search warrant. If you have a cellphone, what the Supreme Court decides will affect you.

Cell companies know where people are
As part of providing their services, cellphone companies know where their users are. Mobile phones connect to nearby towers, which have separate antennas pointing different directions. Noting which antennas on which towers a particular phone connects to allows the phone company to triangulate a fairly precise location.

In addition, technological advances are allowing cell towers to serve smaller and smaller areas. That means connected users are in even more specific locations. The FCC actually requires phone companies to be able to locate most cellphones within fifty meters when they call 911, to be able to direct emergency responders to the correct location.