The Supreme Court on Monday rejected an appeal by Khalid Sheikh Mohammed, the accused mastermind of the September 11, 2001, terrorist attacks, leaving in place the cancellation of a plea agreement that would have spared him the death penalty. The decision clears the way for the military prosecution to proceed toward a trial currently scheduled for June 2028.

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The proposed agreement would have required Mohammed to plead guilty and accept life in prison without the possibility of parole. Two co-defendants, Mustafa al-Hawsawi and Walid bin Attash, also reached plea agreements in 2024 that would have removed the possibility of execution.

Military prosecutors and the Pentagon official overseeing the Guantanamo Bay military commissions approved the deals. However, then-Defense Secretary Lloyd Austin intervened in August 2024, voiding the agreements and arguing that a decision to forgo the death penalty in a case as consequential as the September 11 attacks should rest with the defense secretary.

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Mohammed is accused of helping develop and direct the plot that used four hijacked commercial airliners to attack the United States. Two planes struck the World Trade Center in New York City, another hit the Pentagon, and the fourth crashed in a field in Pennsylvania after passengers fought back against the hijackers.

Defense attorneys challenged Austin’s authority to cancel the deals, arguing that he acted too late and that the agreements should remain binding. A divided federal appeals court ruled that Austin had the authority to withdraw them, and the Supreme Court’s refusal to hear the appeal leaves that ruling in place.

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The agreements divided relatives of September 11 victims. Some argued that a full trial was necessary to deliver justice and establish accountability, while others viewed guilty pleas and life sentences as a way to bring an end to decades of legal proceedings.

The case has faced years of delays since Mohammed and other defendants were charged in the military commission system. The trial is now scheduled to begin in June 2028, more than 26 years after the attacks. With the plea agreements no longer available, Mohammed and the co-defendants could face the death penalty if convicted of capital offenses