By Zachary Fagenson

MIAMI (Reuters) - A U.S. appeals court ruled on Wednesday that cell phone tower tracking data used to convict a Miami man for a string of arm robberies that resulted in a 162-year prison sentence violated his constitutional right of privacy.

The ruling, however, is little relief for 22-year-old Quartavious Davis, whose conviction and sentence were mostly upheld after the court found police and federal prosecutors acted in good faith by seeking permission to access historical cell site data from a federal magistrate judge.

“The government’s warrantless gathering of his cell site location information violated his reasonable expectation of privacy,” federal Judge David Bryan Sentelle wrote on behalf of a three-judge panel of 11th U.S. Circuit Court of Appeals.

The case comes as federal courts around the country wrestle with cell phone privacy issues. Phone data are often used as evidence to show suspects were in the vicinity of a crime.

“This is the first time a court has addressed the Fourth Amendment implications of historic cell phone location tracking based on a factual record that shows how intrusive it was,” Nathan Freed Wessler, an attorney with the American Civil Liberties Union, said on Wednesday.

The court agreed with the ACLU, which argued cell phone location data was protected under the Fourth Amendment of the U.S. Constitution, which bars unreasonable searches and seizures.

The ruling does not prevent police from using the cell phone tower tracking data, but requires them to first obtain a warrant from a judge based on probable cause and not simply a court order based on reasonable suspicion.

The ruling did find in Davis' favor on a minor issue over his sentencing on one count, stating that the evidence did not prove he brandished a gun during a robbery, only that he was in possession of one. Under the sentencing guidelines that would only amount to a two-year sentence reduction.

Davis was convicted in 2010 of carrying a gun during more than a half dozen robberies and sentenced to 1,941 months in prison. The unusually long sentence stemmed from a controversial practice known as "stacking," in which mandatory minimum sentences for each charge are counted consecutively.

(Editing by David Adams and Jim Loney)

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