When the Supreme Court said in United States v. Jones that planting a GPS device on a vehicle is a physical intrusion that amounts to a Fourth Amendment "search," the government should have gotten the memo: the police have to get a probable cause warrant issued by a neutral magistrate before installing one of those devices on a car to track a person's location. Amazingly, that hasn't stopped the government from coming up with new ways to argue that it can use GPS devices to track people's movements without a warrant. So we teamed up with the ACLU and the National Association of Criminal Defense Lawyers in an amicus brief filed last week urging a federal appeals court to reject these arguments.

In the case, United States v. Katzin, FBI agents installed a GPS device on a minivan without a search warrant to track the movements of three brothers suspected of committing a string of robberies. The trial court wouldn't let the government use the the GPS evidence to prosecute the brothers because the government violated the Fourth Amendment when collecting it. The government appealed to the Third Circuit Court of Appeals, arguing that the agents didn't need to get a warrant to gather the GPS evidence because the Supreme Court's decision in Jones held only that warrant is required to install a GPS device, but didn't reach the question of whether a warrant is required to monitor a person's movements using that device. The government also claimed that the officers planted the GPS device before the Supreme Court decided Jones, and so weren't required to get a warrant, since they were relying in good faith on the law as it existed at that time.