Khalid Sheikh Mohammed, seen here shortly after his 2003 capture, has said he planned the September 11 attacks 'from A-Z'

Washington (United States) (AFP) - Khalid Sheikh Mohammed, the alleged mastermind of the September 11, 2001 attacks on the United States, will go on trial before a US military court in June 2028, an official said Thursday.

The long-awaited trial of Mohammed and three other accused ⁹⁄₁₁ plotters is scheduled to begin on June 5, 2028 at the US naval base in Guantanamo Bay, Cuba, a court spokesman said.

Prosecutors had requested a January 2027 date for the trial of Mohammed, Walid bin Attash, Ali Abdul Aziz Ali and Mustafa Ahmed al-Hawsawi but the presiding military judge said more time was needed to resolve pretrial disputes.

Mohammed, also known as “KSM,” was considered one of Al-Qaeda leader Osama bin Laden’s top lieutenants before he was captured in March 2003 in Pakistan.

He was held in secret CIA facilities for three years before arriving at the military prison in Guantanamo Bay in 2006.

Mohammed’s trial has been repeatedly delayed and a plea deal that would have seen the death penalty taken off the table was withdrawn last year following protests from the relatives of some victims of the ⁹⁄₁₁ attacks on New York and Washington.

Much of the legal jousting in the ⁹⁄₁₁ defendants’ cases has focused on whether they could be tried fairly after having undergone torture at the hands of the CIA.

A trained engineer, Mohammed has said he masterminded the ⁹⁄₁₁ attacks “from A to Z” and has claimed involvement in a string of other plots against the United States, where he attended university.

His deadliest was the ⁹⁄₁₁ operation, which saw nearly 3,000 people killed after hijacked planes rammed into the Twin Towers in New York and the Pentagon in Washington, with another crashing in a Pennsylvania field.

Mohammed, born in Kuwait to parents from Pakistan, also claims to have helped in the 1993 World Trade Center bombing that killed six people and to have personally beheaded US journalist Daniel Pearl in 2002.

The United States uses Guantanamo, an isolated naval base, to hold militants captured during the “War on Terror” that followed the ⁹⁄₁₁ attacks in a bid to keep the defendants from claiming rights under US law.

The facility held roughly 800 prisoners at its peak, but they have since slowly been sent to other countries. A small fraction of that number remains.