WASHINGTON (AP) — A divided federal appeals court on Friday threw out an agreement that would have allowed accused Sept. 11 mastermind Khalid Sheikh Mohammed to plead guilty in a deal that would have spared him the risk of execution for al-Qaida’s 2001 attacks.

The decision by a panel of the federal appeals court in Washington, D.C., undoes an attempt to wrap up more than two decades of military prosecution beset by legal and logistical troubles. It signals there will be no quick end to the long struggle by the U.S. military and successive administrations to bring to justice the man charged with planning one of the deadliest attacks ever on the United States.

The deal, negotiated over two years and approved by military prosecutors and the Pentagon’s senior official for Guantanamo a year ago, stipulated life sentences without parole for Mohammed and two co-defendants.

Mohammed is accused of developing and directing the plot to crash hijacked airliners into the World Trade Center and the Pentagon. Another of the hijacked planes flew into a field in Pennsylvania.