New York City police and prosecutors say the encryption in Apple mobile phones is routinely hindering investigations, and they predict the problem could grow worse as more criminals figure out how well the devices keep secrets.
Manhattan District Attorney Cyrus Vance Jr said at a news conference that investigators could not access 175 Apple devices sitting in his cybercrime lab because of encryption embedded in the company's latest operating systems.
"They're warrant-proof," he said, adding the inability to peer inside the devices was especially problematic because so much evidence once stored in file cabinets, on paper and in vaults is now only on criminals' smartphones.
Apple has marketed its encryption data as an important privacy tool, and many privacy advocates have praised the company, saying if it opened its devices to government surveillance then that ability to spy on users could be abused in places with authoritarian regimes.
"There is no magic key that only good guys can use and bad guys cannot," said Cindy Cohn, the executive director of the Electronic Frontier Foundation, which is a digital civil liberties organisation.
"Any vulnerability Apple is forced to create in its phones can and will be exploited by criminals making all less secure," Cohn said. "This is really a question of security versus surveillance."
Apple, based in Cupertino, California, is fighting a federal magistrate's order to help the FBI hack into an iPhone used by a gunman in December's mass shooting in San Bernardino, California.
An Apple spokesman did not immediately return a call Thursday (local time) for comment on the concerns of New York City authorities.
Vance did not specify which cases were being hindered. But Police Commissioner William Bratton said a phone seized in the investigation of the shooting of two police officers in the Bronx in January was among those detectives could not crack.
It was displayed on Thursday alongside other phones, iPads and tablets similar to 600 devices the prosecutor's team tested, of which the 175 proved inaccessible.
Bratton said criminals were increasingly aware of the protection offered by their devices. He said a prisoner in a city jail was recently recorded saying in a phone call that iPhone encryption was "another gift from God".
Vance said investigators had relied on phone data to investigate killings, child pornography, robbery and identity theft. He said that might include checking a suspect's contact list to get the names of witnesses or conspirators, or viewing incriminating videos and photographs.
Apple chief executive Tim Cook has warned that creating software allowing the FBI to unlock the San Bernardino suspect's phone could make millions of other phones vulnerable to hackers and criminals.
Cook said if Apple was forced by the courts to "hack our own users", the government could order the company to build surveillance software to intercept all sorts of messages, "access your health records or financial data, track your location, or even access your phone's microphone or camera without your knowledge".