U.S. border authorities cannot search the cellphones of travelers without having some reason to believe a particular traveler has committed a crime, a federal appeals court ruled Wednesday.

The 4th U.S. Circuit Court of Appeals in Richmond ruled in the case of a Turkish national who was arrested at Dulles International Airport after agents found firearm parts in his luggage.

A lower court judge refused to suppress evidence obtained from a warrantless search of Hamza Kolsuz's phone.

The 4th Circuit upheld that ruling and found that a forensic search of electronic devices requires "individualized suspicion" of wrongdoing. The court said agents had that suspicion because Kolsuz had made two previous attempts to smuggle weapons parts out of the U.S.

The Fourth Amendment requires law enforcement to obtain warrants based on probable cause. But courts have made an exception for searches at airports and U.S. ports of entry, finding that the government can conduct warrantless border searches to protect national security, prevent transnational crime and enforce immigration and customs laws.

The American Civil Liberties had urged the 4th Circuit to find that the government should be required to obtain a warrant or at least a determination of probable cause that evidence of a crime is contained on electronic devices before agents can search them at airports.