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WASHINGTON — The FBI was unable last year to get access to the contents of more than half the electronic devices seized for evidence — a problem that is getting worse, FBI Director Christopher Wray said Tuesday.

Despite having court orders allowing agents to examine the contents of the devices, the FBI was unable to open 7,775 devices in fiscal 2017, which ended in September.

"Each one was tied to a specific subject, a specific defendant, a specific victim, a specific threat," Wray said at a cybersecurity conference at Fordham University in New York.

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A senior FBI official said the share of devices that couldn't be opened is the highest yet. "It's a problem that keeps getting worse," the official said.

Wray said investigating and prosecuting nearly every type of crime now depends on obtaining electronic evidence.

"We're increasingly unable to access that evidence, despite lawful authority to do so," he said.

Wray's comments to the cybersecurity conference expanded on the "going dark" theme first sounded by his predecessor, James Comey, who launched a court fight with Apple to get the contents of a cellphone left behind by one of the San Bernardino terrorists. The FBI eventually opened the device using a technique developed by a private party.

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Wray said more criminals are also using encrypted apps, which allow communications that cannot be monitored or obtained by the FBI even with a court order. The FBI is not looking for a "back door" that would allow agents to obtain the contents of those messages secretly, he said. Instead, law enforcement wants the app developers to obtain the information when presented with a court order.

While some technology experts maintain that developing a way into those communications is impossible, Wray said he is confident American innovation can find the solution. And he noted that in other countries, the tech industry is responding to demands for access to data even though those countries lack the due process guarantees of American courts.

"I just cannot believe that such a paradox is something that anybody really thinks is the right way to go," he said.

Wray said learning about the complexity of the cyber issue has been eye-opening since he last focused on it 12 years ago as a Justice Department official.

In an apparent allusion to President Donald Trump's recent Twitter attacks on the FBI, Wray said: "Back then, social media didn't really even exist. Tweeting was something that birds did. It's a little more on my radar at the moment."