Six relatives of San Bernardino attack victims filed a legal brief on Thursday opposing Apple in its high-profile fight against the U.S. Justice Department's bid to unlock an encrypted iPhone belonging to one of the shooters.

The dispute between Apple and the government burst into the open last month when the Federal Bureau of Investigation obtained a court order requiring Apple to write new software and take other measures to disable passcode protection and allow access to shooter Rizwan Farook's iPhone.

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In the families' brief, they argue that Apple's arguments are misplaced because the government has a valid warrant, and "one does not enjoy the privacy to commit a crime." The families also said Apple "routinely modifies its systems" to comply with Chinese government directives.