The Justice Department argued in a brief filed with a federal appeals court in the District of Columbia that the government would be irreparably harmed if the guilty pleas were accepted for Mohammed and two co-defendants in the Sept. 11, 2001, attacks.

It said the government would be denied a chance for a public trial and the opportunity to “seek capital punishment against three men charged with a heinous act of mass murder that caused the death of thousands of people and shocked the nation and the world.”

The Defense Department negotiated and approved the plea deal but later repudiated it. Attorneys for the defendants argue the deal is already legally in effect and that Defense Secretary Lloyd Austin, who began the administration’s efforts to throw it out, acted too late.

When the appeal was filed Tuesday, family members of some the nearly 3,000 people killed in the al-Qaida attacks already were gathered at the U.S. naval base in Guantanamo Bay, Cuba, to hear Mohammed’s scheduled guilty plea Friday. The other two men, accused of lesser roles in 9/11, were due to enter them next week.

Family members have been split on the deal, with some calling it the best resolution possible for a prosecution mired for more than a decade in pretrial hearings and legal and logistical difficulties. Others demanded a trial and — they hoped — execution.

Some legal experts have warned that the legal challenges posed by the case, including the men’s torture under CIA custody after their capture, could keep the aging detainees from ever facing verdicts and any possible sentences.

Military prosecutors this summer notified families of the victims that the senior Pentagon official overseeing Guantanamo had approved a plea deal after more than two years of negotiations. The deal was “the best path to finality and justice,” military prosecutors said.

But some family members and Republican lawmakers condemned the deal and the Biden administration for reaching it.

Austin has fought unsuccessfully since August to throw out the agreement, saying that a decision on death penalties in an attack as grave as the Sept. 11 plot should only be made by the defense secretary.

A military judge at Guantanamo and a military appeals panel rejected those efforts, saying he had no power to throw out the agreement after it had been approved by the senior Pentagon official for Guantanamo.

Defense attorneys say the plea agreement was approved by Austin’s own officials and military prosecutors and that his intervention was unlawful political interference in the justice system.

The Justice Department brief Tuesday said the defendants would not be harmed by a short delay, given that the prosecution has been ongoing since 2012 and the plea agreements would likely result in them serving long prison sentences, potentially for the rest of their lives.

“A short delay to allow this Court to weigh the merits of the government’s request in this momentous case will not materially harm the respondents,” the government argued.

The Justice Department criticized the military commission judge for a ruling that it said “improperly curtailed” the defense secretary’s authority in a “case of unique national importance.” Preserving that authority “is a matter of critical importance warranting the issuance of extraordinary relief,” the government’s filing said.