The self-confessed mastermind of the 9/11 attacks and four co-accused were due to be arraigned Saturday, May 5 at Guantanamo Bay, with all facing the death penalty if convicted, AFP reports.

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 marks the second time the United States has tried to prosecute the 9/11 suspects.

Mohammed will appear 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 U.S.-run prison in Guantanamo Bay, Cuba, while a legal and political battle has played out over how and where to prosecute them - and debates have raged over how they were treated.

It has been nine years since Mohammed's 2003 arrest, three of which he spent in secret CIA jails, confessing to a series of attacks and plots after being subjected to harsh interrogations, including waterboarding.

Some analysts say Mohammed could try to take advantage of the intense interest in the proceedings to deliver a scathing attack on the U.S. government.

The trial could still be years away, unless Mohammed pleads guilty to be put to death sooner and become a "martyr" for Al-Qaeda.