Kevin Johnson

USA TODAY

WASHINGTON — At the same time the FBI was struggling to unlock the iPhone of San Bernardino terrorist Syed Farook, the agency was being inundated with requests from state and local law enforcement seeking help accessing the contents of hundreds of encrypted or damaged cellphones linked to unrelated criminal investigations scattered across the country.

Requests involving more than 500 such devices streamed into the bureau’s Computer Analysis Response Team and the agency’s Regional Computer Forensic Laboratory programs during a four-month period beginning last October, two months before agents seized Farook’s device in the aftermath of the mass shooting that left 14 dead, according to the FBI.

The numbers, the most recent accounting provided by the agency, offer an assessment —albeit limited — of the mounting investigatory challenges posed by encryption and other technological hurdles beyond the San Bernardino case that launched the government’s recently aborted court battle with Apple Inc.

Last week, a separate survey of more than a dozen state and local law enforcement agencies, based on data gathered by the Manhattan District Attorney's Office and USA TODAY, found that investigators have been blocked from the contents of more than 1,000 smartphones and other devices in recent months.

1,000 locked devices in limbo after FBI quits iPhone case

Many of the devices, manufactured by Apple and other makers, sit in the archives of evidence rooms where authorities were forced to resolve cases without the information contained in the blocked devices. Still other devices are linked to open investigations ranging from shootings and kidnappings to white-collar inquiries.

The FBI, which last week abruptly withdrew from its legal battle to force Apple's assistance in unlocking the Farook phone after getting the help of an undisclosed "outside party,'' said in a statement Wednesday that the mass of recent requests for forensic help have involved efforts to retrieve deleted data, salvage damaged hardware, access encrypted content and bypass locked phones. In the Farook case, investigators had sought Apple's help in bypassing the security function to unlock the device.

FBI hacks into terrorist’s iPhone without Apple

Apple was challenging a federal magistrate's order directing the company to help when the government withdrew from the case after the FBI — with the outside assistance — was finally able to hack into the phone.

In its statement, the FBI said it was responding to the local assistance requests "on a case by case basis, using known forensic tools to assist when appropriate, consistent with our legal and privacy constraints.''

"The FBI is not always able to accommodate the requested assistance,'' according to the statement. And it wasn't immediately clear how many of the hundreds of requests had been addressed or resolved.

After the government announced last week that it had successfully hacked into the Farook phone, the FBI sent a letter to state and local agencies reiterating the agency's pledge to assist when it could.

"We know that the absence of lawful, critical investigative tools due to the 'going dark' problem is a substantial state and local law enforcement challenge that you face daily,'' the FBI said in its Friday bulletin. "As has been our longstanding policy, the FBI will of course consider any tool that might be helpful to our partners.''

However, federal authorities have yet to determine whether the new method used in the San Bernardino case can or will be applied more broadly, two federal law enforcement officials said. The officials, who are not authorized to comment publicly, said the method has not been used so far in another pending case.

And, the officials said, the letter was not meant to suggest that the agency had a key that would suddenly resolve the backlog of pending requests for assistance.

"Please know that we will continue to do everything we can to help you consistent with our legal and policy constraints,'' the FBI told local law enforcement agencies. "You have our commitment that we will maintain an open dialogue. We are in this together.''