On Thursday, FBI director James Comey sharply criticized Apple and Google for developing new forms of smartphone encryption. While user security has been at the forefront of these developments, the manufacture’s have created algorithms that are so secure that law enforcement officials cannot easily gain access to information stored on the devices, even when they have valid search warrants.

“There will come a day when it will matter a great deal to the lives of people … that we will be able to gain access” to such devices, Mr Comey told reporters in a briefing. “I want to have that conversation [with companies responsible] before that day comes.”

His comments echo statements from law enforcement officials across the United States. Police have said that the ability to search photos, messages and web histories on smartphones is essential to solving a range of serious crimes, from murder to child pornography to attempted terrorist attacks. Easy access to smartphones by law enforcement may be drawing to a close as tech companies erect new security barriers.

Mr Comey’s remarks followed news last week that Apple’s iOS 8 is so thoroughly encrypted that the company is unable to unlock iPhones or iPads for police. Google, meanwhile, is moving to an automatic form of encryption for its newest version of the Android operating system. Police frustration is high towards Apple, which is moving swiftly the encryption enabled devices to consumers.

“Apple will become the phone of choice for the pedophile,” said John J, Escalante, chief of detectives for Chicago’s police department. “The average pedophile at this point is probably thinking, I’ve got to get an Apple phone.”

For detectives working a tough case, few types of evidence are more revealing than a smartphone. Calls logs, instant messages and location records can link a suspect to a crime precisely when and where it occurred. And a surprising number of criminals take selfies posing with accomplices and often the loot they stole together.

The devices are now moving beyond the reach of police use. The result, say law enforcement officials, legal experts and forensic analysts, is more seized smartphones will end up as shiny paperweights, with incriminating evidence locked inside.

Both companies declined to offer immediate reaction to Mr Comey’s comments.