Khalid Sheikh Mohammed
File photo of Khalid Sheikh Mohammed Reuters

High drama unfolded at the U.S. base in Guantanamo Bay, Cuba, as the trial of five men accused in the 9/11 attack, including alleged mastermind Khalid Sheikh Mohammed, began.

The self-confessed mastermind of the attack and four others refused to answer questions during the 13-hour hearing on the opening day of the trial on Saturday.

The charges for the terrorist the attack that killed 2,976 people could get them the death penalty.

The military tribunal was adjourned until June 12. Defense lawyers raised doubts about the legitimacy of the court.

All the five accused will be asked once again to enter pleas of guilty or not guilty during a later hearing.

Defense lawyer David Nevin told the court that "the world is watching" the trial, reported the Guardian. "[The tribunal] is a blight on America's international reputation and her commitment to the rule of law," the newspaper quoted another defense lawyer, James Connell, as saying.

Khalid Sheikh Mohammed, Waleed bin Attash, Ramzi Binalshibh, Ali Abd al-Aziz Ali and Mustafa Ahmad al-Hawsawi each face charges of 2,976 murders (the victims of the 9/11 attack) and also conniving with the late al Qaeda leader Osama bin Laden in the act of terrorism, hijacking and destruction of property.

One of the accused remained restrained in his chair while another prayed in the court for several minutes, delaying the hearing.

Later all the defendants refused to wear the headphones provided for Arabic translation of the proceedings.

Ramzi Binalshibh tried to interrupt the court during the proceedings and the judge told him to speak later to which he replied: "Maybe you're not going to see us anymore. Maybe they will kill me and say I committed suicide," according to a BBC report.

In 2008, Mohammed said he would plead guilty provided he was tried as a martyr and not as a terrorist.

The defendant has been alleging that he was tortured during his detention and CIA documents also confirmed waterboarding him 183 times.

The Obama adminstration's attempt to shift the trial to a civilian court in the U.S. failed in the face of widespread opposition.