Five men accused of plotting the 9/11 terrorist attacks have been brought before a US military tribunal in Guantanamo Bay in Cuba.
Khalid Sheikh Mohammed, the self proclaimed mastermind behind the attacks, is among those before the inquiry.
The men face a number of charges, including terrorism, conspiracy and murder.
Relatives of those killed in the hijacked plane attacks in New York and in Washington DC in September 2001 attended the proceedings.
All five defendants refused to answer the judge's questions and one made outbursts in court.
Defense lawyers answered routine questions about their resumes with complaints that the proceedings were unfair and that the defendants had been abused.
"I believe Mr Mohammed will decline to address the court. I believe he's deeply concerned about the fairness of the proceeding," said his civilian lawyer, David Nevin.
The military tribunal hearing on charges that include murdering 2,976 people marked the first time Mr Mohammed and his four co-defendants had been seen in public in about three years.
They are accused of conspiring with Osama bin Laden, murder in violation of the laws of war, hijacking, terrorism and other charges.
A previous attempt to prosecute them in the Guantanamo war crimes tribunal was halted when the Obama administration tried unsuccessfully to move the case into a New York federal court.
Yemeni defendant Ramzi Binalshibh knelt on the gray-carpeted courtroom floor and prayed as a row of burly guards in camouflage uniforms kept a close watch but did not interfere.
Later he stood and shouted, and seemed to be saying that the late Libyan leader Muammar Gaddafi was being held at Guantanamo.
He said tricks were being played on the defendants inside the prison camp and that "maybe they are going to kill us at the camp ... and say that we are committing suicide."
Yemeni defendant Walid bin Attash refused to come into the court and was strapped into a restraining chair and wheeled in by the guards.
His prosthetic leg was brought in later. It replaces the right leg he lost during a 1997 battle in Afghanistan.
The judge later freed him from the chair after he promised to behave inside the courtroom.
The defendants refused to listen through earphones to English-Arabic translations of the judge's questions.
The judge recessed the hearing and then resumed it with an interpreter providing a translation that was broadcast over a loudspeaker into the court, sometimes drowning out the conversation between the lawyers and the judge.
Cheryl Borman, a civilian attorney for Bin Attash, wore a black hijab and long black robe and told the court that the treatment of her client at Guantanamo had interfered with his ability to participate in the proceedings.
"These men have been mistreated," Ms Borman said.
The judge said that until the question of the men's legal representation was settled, the attorneys had no standing to raise other issues.
The defendants prayed and chatted among themselves during recesses, and passed around a copy of The Economist magazine.
But they refused to answer the judge's questions. He ruled that they would be represented by the lawyers assigned to them.
In addition to their military lawyers, each has a civilian attorney with experience in death penalty cases.
