The government's filing is aimed at encouraging a federal magistrate judge to affirm her order from last month that directed Apple to help the FBI gain access to the phone used by Syed Farook, one of the two attackers in the December 2 shootings that killed 14 people.
"There is probable cause to believe there is evidence of a terrorist attack on that phone, and our legal system gives this Court the authority to see that it can be searched pursuant to a lawful warrant," the filing states.
At issue is a February 16 order directing Apple to create specialised software that can bypass auto-erase functions on the phone and enable the FBI to remotely access the phone.
Apple has challenged the order as unlawful and in violation of its constitutional rights, but the Justice Department reiterated its argument that its request is only about one phone and that it will not be unduly burdensome for the company to comply.