Khalid Sheikh Mohammed, the self-proclaimed mastermind behind the attacks, and his co-defendants appeared for the first time in more than three years for arraignment at a military tribunal at Guantanamo Bay, charged with 2,976 counts of murder for the 2001 attacks.
Even before they could be arraigned, the men took off their earphones that provide Arabic translations and refused to answer any questions from the judge, Army Col. James Pohl, dramatically slowing a hearing that is heavy on military legal procedure.
At one point, two defendants got up and prayed at their defense tables. They refused to participate in the hearing. Pohl warned he would not permit defendants to block the hearing and would continue without their participation.
Since the men weren't wearing their earpieces, the judge brought the translators into the court room. Still, the prisoners refused to answer any questions. They didn't even acknowledge that they understood the questions.
In the past, during the failed first effort to prosecute them at the U.S. base in Cuba, Mohammed has mocked the tribunal and said he and his co-defendants would plead guilty and welcome execution. But there were signs that at least some of the defense teams were preparing for a lengthy fight, planning challenges of the military tribunals and the secrecy that shrouds the case.
The men have not been seen in public since a pretrial hearing the day after President Barack Obama's inauguration in 2009.
Some family members of victims participated in a lottery to get a chance to go to the base and watch the arraignment in person.
Others gathered at military bases in New York and across the East Coast to watch on closed-circuit TV. Mohammed, a Pakistani citizen who grew up in Kuwait and attended college in Greensboro, North Carolina, has admitted to military authorities that he was responsible for the Sept. 11 attacks as well as about 30 other plots, and that he personally killed Wall Street Journal reporter Daniel Pearl. Mohammed was captured in 2003 in Pakistan.
His four co-defendants include Ramzi Binalshibh, a Yemeni, who was allegedly chosen to be a hijacker but couldn't get a U.S. visa and ended up providing assistance such as finding flight schools; Waleed bin Attash, also from Yemen, who allegedly ran an al Qaeda training camp in Afghanistan and researched flight simulators and timetables; Mustafa Ahmad al-Hawsawi, a Saudi accused of helping the hijackers with money, Western clothing, traveler's checks and credit cards; and al-Aziz Ali, a Pakistani national and nephew of Mohammed, who allegedly provided money to the hijackers.
The Associated Press contributed to this report.