In a case handed down on Friday, a federal appeals court has ruled that police may not use a global positioning satellite (GPS) unit to track a person’s movements for a long period of time without a warrant. Doing so violates a person’s Fourth Amendment right to be free of unreasonable search and seizure, the court said (.pdf) [1].

In the case, U.S. v. Maynard, Washington D.C. police were investigating Antoine Jones on suspicion of distributing cocaine. Police attached a GPS unit to Jones’s car and tracked his movements continuously for a month. Based on this information, police arrested Jones and convicted him on several drug charges.

Jones, along with his co-conspirator Lawrence Maynard, filed a lawsuit against the city arguing that the GPS information was obtained illegally. The city argued that it relied on case law established in U.S. v. Knotts, a 1982 case in which the court ruled that the police did not commit a search when it placed a beeper in a container to track a suspect's movements from one place to another. In that case, the court ruled that a warrant was unnecessary.

In the current case, the court ruled that the Knotts case does not apply. According to the court, the limited information obtained by determining a suspect’s movements from one point to another in public is not the same as using a GPS to track every trip a suspect makes and then aggregating that data. Prolonged surveillance, ruled the court, reveals much more information and requires a warrant.

In the written opinion of the case, the court noted that “repeated visits to a church, a gym, a bar, or a bookie tell a story not told by any single visit…a single trip to a gynecologists office tells little about a woman, but that trip followed a few weeks later by a visit to a baby supply store tells a different story.”

The case against Jones, ruled the court, used the pattern of the suspect’s movements to establish guilt. Because such information was obtained in violation of the Fourth Amendment, the court ruled that the case must be thrown out.

♦ Photo of GPS tracking by aaronparecki/Flickr [2]

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