The US Supreme Court has ruled that police officers usually need a warrant before they can search the cellphone of a suspect, a major decision in favour of privacy rights at a time of increasing concern over government encroachment in digital communications.
In an opinion written by Chief Justice John Roberts, the court said there are some emergency situations in which a warrantless search would be permitted. But the unanimous 9-0 ruling goes against law enforcement agencies including the US Department of Justice, which wanted more latitude to search without having to obtain a warrant.
"We cannot deny that our decision ... will have an impact on the ability of law enforcement to combat crime," Roberts wrote, adding that the right to privacy "comes at a cost".
Roberts acknowledged the unique nature of cellphones in contemporary life, noting that "the proverbial visitor from Mars might conclude they were an important feature of human anatomy".
"The fact that technology now allows an individual to carry such information in his hand does not make the information any less worthy of the protection for which the [country's] founders fought. Our answer to the question of what police must do before searching a cellphone seized incident to an arrest is accordingly simple - get a warrant," Roberts wrote.
The ruling could have a major impact in some jurisdictions because law enforcement agencies have increasingly made cellphone searches a priority when a suspect is arrested, said Bronson James, a criminal defence attorney in Portland, Oregon.
"Police wanted the data on the cellphones because it was so expansive," he said. "This stops that practice."
The implications may be limited by the fact that police can benefit from new technology: it is now possible to obtain a warrant more quickly using mobile devices to send the request.
But the ruling could hamper law enforcement when there is a need to gather information from a cellphone immediately because of an ongoing criminal enterprise, said Robert Mintz, a former federal prosecutor. "There could be circumstances when news of an arrest can travel quickly and time could be of the essence," he said.
Justice Department spokeswoman Ellen Canale said the government would ensure federal law enforcement agents complied with the ruling.
The court was considering two separate cases pitting evolving expectations of privacy against the interests of the law enforcement community as the justices for the first time weighed the ubiquitous role of cellphones in modern life.
The defendants challenging their convictions, David Riley and Brima Wurie, said evidence found on their phones should not have been used at trial because the searches were conducted without court-issued warrants.
The circumstances in the two cases, one from Massachusetts and one from California, were different in terms of the scope of the search and the type of cellphone used. Wurie had a basic flip phone while Riley had a more sophisticated smartphone.
The court decided the two cases together, finding that both searches were unconstitutional.
Riley was convicted of three charges relating to a 2009 San Diego incident in which shots were fired at an occupied vehicle. Prosecutors linked him to the crime in part based on a photo police found on his smartphone.
Police searched Wurie's cellphone without a warrant after his 2007 arrest for suspected drug dealing. Officers found a phone number that took them to his house in Boston, where drugs, a gun and cash were found.
A Reuters/Ipsos opinion poll found 60.7 per cent of people surveyed said police should not be allowed to search cellphones without a warrant.