The self-confessed mastermind of the 9/11 attacks and four co-accused plotters were arraigned on May 5 at Guantanamo Bay, with all facing the death penalty if convicted.
Khalid Sheikh Mohammed and his co-defendants will be formally charged in a military tribunal with planning and executing the September 11, 2001 attacks that killed 2,976 people in New York, Washington and Shanksville, Pennsylvania.
One of the last steps before the so-called “trial of the century” takes place, the arraignment marked the second time the United States has tried to prosecute the 9/11 suspects.
It comes more than a decade after the most lethal attacks on US soil in modern history, and just about one year after President Barack Obama ordered the US Navy SEALs raid that killed the man behind it all; Osama bin Laden.
“There is a desire for justice, it is an important moment for all of us,” said Marc Thiessen, a former speechwriter for president George W. Bush who has defended the Bush administration's use of enhanced interrogation techniques on terror suspects.
Mohammed appeared in the military tribunal along with Ramzi Binalshibh of Yemen, Mohammed's Pakistani nephew Ali Abd al-Aziz Ali, also known as Ammar al-Baluchi; Walid bin Attash and Mustapha al-Hawsawi of Saudi Arabia.
The five have been held for years at the US-run prison in Guantanamo Bay, Cuba, while a legal and political battle has played out over how and where to prosecute them.
It has been nine years since Mohammed's arrest, three of which he spent in secret CIA jails, confessing to a series of attacks and plots after being subjected to harsh interrogations.
Out of 200 applicants, 60 journalists had obtained seats for the hearing at the US naval base in southern Cuba, while another 30 will cover the event from Fort Meade in Maryland using a closed-circuit television feed.
“It's key to have transparency,” the military commission's chief prosecutor, Brigadier General Mark Martins, told AFP.
But after a hearing lasting more than nine hours, Mohammed and his four co-defendants opted not to plead innocent or guilty but rather to push back their plea to a later date.