Federal investigators have offered few details about how they gained access to Farook's phone. The iPhone 5c was at the center of a court battle between the FBI and Apple, which led to a court order that Apple create software that would allow the FBI to access encrypted data on the device.
Farook disabled the phone's iCloud backup feature six weeks before the Dec. 2 attack, according to court filings. He had also enabled an auto-erase feature that would permanently destroy all data on the phone after 10 consecutive failed attempts to enter the device's password.
A third party provided the FBI with a way to disable the password entry limit, according to another law enforcement official with knowledge of the investigation who was not authorized to discuss the case and spoke on the condition of anonymity.
Internal government policy might limit what, if anything, the FBI could share about the method used to hack Farook's phone, said Andrew Crocker, a staff attorney with the Electronic Frontier Foundation, a digital rights advocacy group.
If the government exploited a flaw in Apple's security measures, it could be required to disclose that information to Apple under the Vulnerabilities Equities Process, Crocker said. The policy is weighted toward disclosure, but the government has successfully fought to keep such details secret before.
Government agencies are allowed to share information about digital security flaws with one another, he said. But if the government chose not to share that information with Apple, it could also conceivably be barred from telling police agencies about the process used to unlock Farook's phone.
“They certainly can share it within the federal government without disclosing it to Apple,” Crocker said. “The way I read the policy, sharing it with local police would be a dissemination outside the government.”
In the Arkansas case, Cody Hiland, prosecuting attorney for the state's 20th Judicial District, said the FBI's Little Rock field office had agreed to help prosecutors gain access to a pair of locked devices linked to suspects in the slayings of Robert and Patricia Cogdell.
Calls to the FBI's Little Rock field office were not immediately returned. An FBI spokesman in Washington, D.C., declined to comment.
Attorneys for Apple are researching legal tactics to compel the government to tell the company what, if any, flaws it exploited in gaining access to Farook's phone. But most experts believe the FBI has no obligation to comply. The FBI could also argue that the most crucial information is part of a nondisclosure agreement, solely in the hands of the outside party that assisted the agency, or cannot be released until the investigation is complete.
Though the debate over Farook's phone did not land in criminal court, the fight between law enforcement and Silicon Valley over access to encrypted data is far from over. The FBI may have claimed a victory this week, but some police leaders fear it won't take long for Apple or another company to build tougher encryption methods.
“If the FBI did in fact find some type of a flaw that they were able to exploit, clearly the industry is going to say, ‘We've got to find a way to plug that hole,'” Cunningham said.