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A critical Supreme Court ruling at the intersection of modern technology and privacy leaves open whether police can still track the car or cell phone of a suspect without threatening their constitutional rights, according to a new report [PDF] from the Congressional Research Service.

Investigators in 2004 secretly affixed a tracking device to the car of nightclub owner Antoine Jones, without a timely warrant, to gather evidence on his role in a drug-trafficking scheme. Jones appealed his resulting life sentence and won when the District of Columbia Circuit Court of Appeals found that data generated from the technology violated his reasonable expectation of privacy under the Fourth Amendment.

The government continued fighting and in the process made his case among the most high profile in recent years by asking the Supreme Court to keep his conviction intact. In a rare unanimous decision, the justices upheld the lower court ruling, but created confusion about whether police will need a warrant in future GPS tracking cases, the research service concluded.

Jim Dempsey, public policy vice president at the Center for Democracy & Technology in San Francisco, said that even though the absolute need for a warrant is uncertain, police will be reluctant to take risks if it could lead to the case being thrown out later. The ruling does raise questions about radical new technologies being pursued by police, such as pilotless drones, he said.  

“Up until now, the law has been that whatever you can see with the naked eye or technology aiding the human eye from the air is not protected,” Dempsey said. “So looking into someone’s backyard from an airplane overhead – not a search. … Positioning a drone over your house 24/7 might be a search.”

Reports from the Congressional Research Service are prepared for Washington lawmakers and their staff and are not technically public. But they’ve long been spirited into the public realm by academics and public-interest groups who consider their neutral tone and insight valuable.

By now, it’s common for police to surreptitiously use Global Positioning Systems, or GPS, to enforce the law. Until the Jones case, however, longer-term monitoring had not been addressed by the Supreme Court.

“Thus,” says the research service, “many observers awaited the Jones ruling for its potential impact not only on government monitoring programs, but also on general Fourth Amendment cases involving prolonged government surveillance.”

Privacy is often at the core of public debate about law enforcement technology and its acceptable use in investigations. But the majority of Supreme Court justices, led by Justice Antonin Scalia, also focused on whether the target vehicle could be considered an “effect,” as in the Fourth Amendment protection of “persons, houses, papers and effects” against unreasonable searches and seizures.

“The majority contended that Jones’s rights should not strictly depend on whether his reasonably expected zone of privacy was pierced,” states the report. “Rather, the majority asserted, property rights also define an individual’s right to be free from government intrusion.”

Blaring news headlines initially declared that a warrant would now be necessary for GPS tracking. The ruling in fact appeared to raise as many questions as it answered, and experts are still not sure how it will be interpreted, due in part to the justices agreeing with one another for different reasons.

If the Jeep driven by Jones is considered an “effect,” does the same hold true for computer data, which police now routinely use in criminal investigations? Do your e-mails amount to electronic paper? If products arrive in the hands of consumers with GPS technology already installed, can police exploit it remotely without touching your effects?

“There are no easy answers to these questions,” say congressional researchers.

In the meantime, government lawyers “scrambled” prior to the Supreme Court decision to get warrants for 3,000 GPS devices that were being used by the FBI, National Public Radio reported in late March. Some 250 of those still had to be turned off.

FBI director Robert Mueller suggested to the House Appropriations Committee earlier this year that the ruling could undermine terrorism investigations, but it’s unclear how many national security cases hinge on GPS tracking, as opposed to drug and gang-related probes.  

“Putting a physical surveillance team out with six, eight, twelve persons is tremendously time-intensive,” Mueller testified in March. “And so it will inhibit our ability to use this in a number of surveillances where it’s been tremendously beneficial. We have a number of people in the United States whom we could not indict – there’s not probable cause to indict them or to arrest them – who present a threat of terrorism.”

G.W. Schulz is a reporter for Reveal, covering security, privacy, technology and criminal justice. Since joining The Center for Investigative Reporting in 2008, he's reported stories for NPR, KQED, Wired.com, The Dallas Morning News, the Chicago Tribune, the San Francisco Chronicle, Mother Jones and more. Prior to that, he wrote for the San Francisco Bay Guardian and was an early contributor to The Chauncey Bailey Project, which won a Tom Renner Award from Investigative Reporters and Editors in 2008. Schulz also has won awards from the California Newspaper Publishers Association and the Society of Professional Journalists’ Northern California Chapter. He graduated from the University of Kansas and is based in Austin, Texas.