PHILADELPHIA — A full U.S. appeals court gathered Wednesday to hear arguments on whether police need a warrant to put a GPS tracking device on a suspect’s car.

The case involves a series of pharmacy robberies near Philadelphia and pits the power of new technology against a person’s right to privacy.

Previous courts ruled that the FBI should have gotten a warrant before using a device that could track a vehicle’s every move for days or weeks.

“These are the types of decisions that should be made by judges,” lawyer Catherine Crump argued Wednesday for the American Civil Liberties Union.

Technology law was in flux when authorities were investigating the pharmacy robberies in 2010, she said, and agents should have proceeded with caution. The agents sought advice from a federal prosecutor, but not the neutral view of a magistrate who issues search warrants, the 3rd U.S. Circuit Court of Appeals judges noted.

However, prosecutors argued that time is sometimes of the essence, and that police believed their actions were legal, given the evolving law.

The case began when state police investigating the burglaries found tools, gloves and a ski mask in a search of electrician Harry Katzin’s van in 2010. He said they were work tools and was let go. But police, working with the FBI, soon put a GPS device under his bumper and closed in on the van after another burglary. They found Katzin and his brothers Mark and Michael inside, along with a large stash of pills, cash and other store property.

However, the evidence found in the van was thrown out, because the trial judge deemed the warrantless use of GPS was an illegal search.