The five 9/11 accused took a path of "peaceful resistance" at a marathon Guantanamo hearing to protest years of torture and inhumane treatment, their lawyers said Sunday.
Confessed mastermind Khalid Sheikh Mohammed and his four alleged co-plotters opted to defer their pleas at Saturday's arraignment proceedings in a 13-hour hearing at the US naval base in Guantanamo Bay, Cuba.
And they repeatedly refused to answer questions, with two men interrupting the hearing to stand up and pray.
"The accused participated in peaceful resistance to an unjust system," lawyer James Connell, who is defending Pakistani Ali Abd al-Aziz Ali, told reporters.
"The accused refused to acknowledge the legitimacy of the military commissions as demonstrated through their silence," he added.
"These men have endured years of inhumane treatment and torture. This treatment has had serious long-term effects and will ultimately infect every aspect of this military commission tribunal."
Mohammed, a Kuwait-born Pakistani, was waterboarded 183 times during the three years he was held in secret CIA prisons after his 2003 capture in Pakistan. He was eventually transferred to Guantanamo in 2006.
He was also deprived of sleep for 7.5 days in a row, while his alleged co-plotters were also subjected to harsh interrogation techniques.
Mohammed, 47, was charged Saturday for his role in the terror attacks by Al-Qaeda militants in which hijacked planes were used to strike New York, Washington and Shanksville, Pennsylvania, killing 2,976 people.
He was formally arraigned along with his nephew Ali, also known as Ammar al-Baluchi; Mustapha al-Hawsawi of Saudi Arabia; and Yemenis Ramzi Binalshibh and Walid bin Attash, who grew up in Saudi Arabia.
After defying the court for more than nine hours by keeping silent, Mohammed and the co-defendants -- in their first public appearance in three years -- finally deferred their pleas.
Dressed in white jumpsuits, with some wearing white turbans, the men mostly refused to engage with the court officials -- reading what looked to be the Koran, keeping their eyes fixed on the ground or kneeling to pray.
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The defendants also passed a copy of The Economist magazine among themselves.
But in one shocking moment, bin Attash took off his top tunic to reveal deep scars on his body. His lawyer, Cheryl Borman, told reporters he had similar marks on his arms, saying she had good reason to believe he had received them at Guantanamo.
He also refused to wear headphones through which a simultaneous translation of the proceedings in Arabic was provided, as it reminded him of his tough interrogations.
Chief prosecutor Brigadier General Mark Martins gave assurances that no evidence elicited under harsh interrogations would be used.
"It's not possible to untaint the evidence," insisted lawyer David Nevin, who is defending Mohammed. "The very first thing that needs to be explored is torture.
"It's not possible to torture someone and at some point of the road say everything we went through is clear. My client has been tortured. The US government, my country, tortured this man," he added.
The defendants were charged with "conspiracy, attacking civilians, murder and violation of the law of war, destruction, hijacking and terrorism" in connection with the attacks, the most lethal on US soil in modern history.
If convicted they face the death penalty.
"Now the government wants to kill Mr Mohammed. They want to extinguish the last witness that has been tortured so he can never speak again," alleged Nevin.
Lawyers also argued that they had not been given the full means to defend their clients, saying they could not communicate effectively with them.
"If I give you a gun to defend your home and I don't give you any bullet, it is the same thing," argued Walter Ruiz, who is defending Hawsawi.
But Martins said "this forum is a lawful means of subjecting to a rigorous and fair criminal trial those alleged to have violated the laws of war."
"We're balancing fair trial, free press and national security," he added.