A divided U.S. appeals court on Wednesday said the government needs a warrant to obtain a suspect's historical cellphone location records.
The 2-1 decision by the 4th U.S. Circuit Court of Appeals in Richmond, Virginia, was a victory for advocates of privacy rights for cellphone users.
It also creates a split with two other federal appeals courts that have decided similar cases, increasing the potential that the U.S. Supreme Court may take up the issue.
Last month, the American Civil Liberties Union appealed one of those decisions, a May 5 ruling from the 11th Circuit Court of Appeals in Atlanta, to the Supreme Court.
Wednesday's decision arose from several armed robberies in Baltimore and Baltimore County, Maryland, in early 2011, leading to the convictions of Aaron Graham and Eric Jordan.
The convictions were based in part on data the government obtained from cellphone provider Sprint/Nextel pursuant to court orders, but without warrants.
Writing for the majority, Circuit Judge Andre Davis said the searches were unreasonable, and thus violated the Fourth Amendment of the U.S. Constitution.
Obtaining a person's historical cellphone location records "can enable the government to trace the movements of the cell phone and its user across public and private spaces and thereby discover the private activities and personal habits of the user," Davis wrote. "Cell phone users have an objectively reasonable expectation of privacy in this information."
Even so, the 4th Circuit refused to void the convictions, saying the government relied in "good faith" on the court orders, triggering an exception to the warrant requirement.
The U.S. Department of Justice, which argued on the government's behalf, did not immediately respond to a request for comment.
"Today's opinion is a full-throated defense of Fourth Amendment privacy rights in the digital age," Nathan Freed Wessler, a lawyer with the ACLU Speech, Privacy, and Technology Project, said in a statement.
Circuit Judge Diana Gribbon Motz dissented. She said it is for the Supreme Court to update the "third-party" doctrine, which suggests that individuals lack reasonable expectations of privacy in records of third parties such as phone companies.
"Time may show that my colleagues have struck the proper balance between technology and privacy," she wrote. "Today the majority endeavors to beat the Supreme Court to the punch."
The cases are U.S. v. Graham, 4th U.S. Circuit Court of Appeals, No. 12-4659, and U.S. v. Jordan in the same court, No. 12-4825.