"We're seeing more and more cases where we believe significant evidence resides on a phone or a laptop, but we can't crack the password," FBI Director Jim Comey said during a speech in Washington. "If this becomes the norm ... justice may be denied."
Specifically, Comey said he is "deeply concerned" about what's known as "going dark" -- operating systems being developed by companies such as Apple and Google that automatically encrypt information on their devices. And that means even the companies themselves won't be able to unlock phones, laptops and other devices so law enforcement can access emails, photos or other evidence that could be crucial to a case, according to Comey.
It "has created a significant public safety problem," particularly when it comes to investigating crime and stopping terrorist attacks, he said.
"Criminals and terrorists would like nothing more than for us to miss out,"Comey said. "And the more we as a society rely on these devices, the more important they are to law enforcement and public safety officials."
Comey, however, didn’t place full blame with companies like Apple and Google for creating devices with such encryption. They were "responding to what they perceive is a market demand" from the general public, which has grown "mistrustful of government" in the wake of Edward Snowden's disclosures of secret government surveillance.
Comey said the public has come to believe "a fair number of misconceptions" about what information the government collects and how it's collected.
"Some believe that the FBI has these phenomenal capabilities to access any information at any time," he said. "It may be true in the movies or on TV. It is simply not the case in real life."
In real life, he said, the government's collection activities are executed "with clear guidance and strict oversight," and with a federal judge's approval.
Asked about Comey’s remarks, Google said its emerging products will provide "added security" to users "while giving law enforcement appropriate access when presented with a warrant."
"Encryption is simply the 21st century method of protecting personal documents," a Google spokesperson said in a statement. "[And] while we won't be able to provide encryption keys to unlock phone data directly, there are still a number of avenues to obtain data through legal channels."
One possible way to still obtain a user's data is through “the cloud” -- but a user has to be uploading information to it for that to be effective. Data on the phone itself, however, cannot be unencrypted by even Google or other companies, one business insider said.
Accordingly, Comey insisted that even if a judge gives the government a green light to access certain information or communications, "we often lack the technical ability to do so."
Privacy advocates in Washington objected to Comey’s remarks, with the American Civil Liberties Union calling them “wrong” and the Electronic Privacy Information Center calling them “surprising” and “disturbing.”
The American Civil Liberties Union said law enforcement can do its job while also respecting Americans’ privacy rights, noting that U.S. law “explicitly” gives companies the right to add completely secure encryption into their devices.
He urged the public to debate whether U.S. law should require technology companies to build lawful intercept capabilities into their devices.
"We aren't seeking to expand our authority to intercept communications. We are struggling to keep up with changing technology," Comey said.
"If a suspected criminal is in his car, and he switches from cellular coverage to Wi-Fi, we may be out of luck," Comey added. "If he switches from one app to another, or from cellular voice service to a voice or messaging app, we may lose him. What if he has a kidnapped child in his car? We may not have the capability to quickly switch lawful surveillance between devices, methods and networks. The bad guys know this. They're taking advantage of it every day."
Comey cited several real-world examples to illustrate what's at stake, including a case fully adjudicated this year involving a known sex offender in Louisiana who enticed a 12-year-old boy to meet him and then killed the boy. The suspect tried to alter and delete evidence on his phone, but authorities were able to access the content and prosecute him. He was sentenced to death in April.
Asked by ABC News whether he knew of any real-world cases where someone was rescued from danger but might not have been had Apple or Google devices blocked law enforcement access, Comey said he did not know of any but added, "Logic tells me there are going to be cases just like that."
Comey’s remarks came hours before Apple announced a slate of new products and software at an event at its corporate campus in Cupertino, California.
Apple did not immediately respond to emails from ABC News seeking comment for this article.