The Justice Department took off the gloves in its latest volley against Apple and its refusal to comply with a court order to unlock a terrorist’s iPhone.

“Apple deliberately raised technological barriers that now stand between a lawful warrant and an iPhone containing evidence related to the terrorist mass murder of 14 Americans,” wrote attorneys for the DoJ on Thursday. “Apple alone can remove those barriers so that the FBI can search the phone and it can do so without undue burden.”

Edward J. McAndrew of D.C. law firm Ballard Spahr, a former federal cybercrime prosecutor, said the aggressive and adversarial nature of the Justice Department’s tone is unusual.

“It’s really strong language and meant to express not just the government’s strength of position, but its sense of outrage over the position Apple has taken,” Mr. McAndrew said.

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