The FBI didn't directly contest that, but argued that there was probably more information on the iPhone 5C than could be gathered from an iCloud backup.
"It is unknown whether an additional iCloud backup of the phone after that date [of Oct. 19, 2015] -- if one had been technically possible -- would have yielded any data," the agency acknowledged. "[But] even if the password had not been changed and Apple could have turned on the auto-backup and loaded it to the cloud, there might be information on the phone that would not be accessible without Apple's assistance as required by the All Writs Act order, since the iCloud backup does not contain everything on an iPhone."
The latter -- that there may be a wealth of information not included in the backup -- has been a point the Department of Justice (DOJ) has made repeatedly in its filings with the federal court that has ordered Apple to help investigators access the phone.
Authorities want Apple to create a modified version of iOS that disables an auto-erase feature -- triggered after 10 incorrect passcode entries -- and removes the forced delays between passcode guesses. The FBI would then conduct a brute-force passcode crack from a personal computer at high speeds to uncover the passcode -- which unlocks the device -- and so examine all the data there.
Apple must be the one that crafts such a tool since only updates signed by the company's digital certificate will be accepted by an iPhone.
Even if resetting the iCloud password was a mistake, the FBI said, Apple remains obligated to assist. "The reset of the iCloud account password does not impact Apple's ability to assist with the the court order under the All Writs Act," said the agency, referring to the 1789 law cited by the DOJ when it asked a federal judge to force Apple to help.
"As the government's pleadings state, the government's objective was, and still is, to extract as much evidence as possible from the phone," the FBI added. "Through previous testing, we know that direct data extraction from an iOS device often provides more data than an iCloud backup contains."
It's possible that Farook turned off the iCloud auto-backup at some point after Oct. 19, although he used the phone after that date, the FBI said. He may also not have charged it when a known Wi-Fi network was available.
Apple has said it will not comply with the court's order to assist the FBI because it would set what it called "a very dangerous precedent." Apple has until Friday to file its objections with the California federal court. That court has set a March 22 date for oral hearings, and will accept amicus briefs from interested parties until March 3.
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