Khalid Sheikh Mohammed is said to be al-Qaeda's number three
The alleged mastermind of the 9/11 attacks on the US and four other key suspects have appeared at a military tribunal in Guantanamo Bay.
Khalid Sheikh Mohammed, who was captured in Pakistan in 2003, dismissed the trial as an "inquisition".
He said he had had five years "under torture" and wished to become a martyr.
All five men face the death penalty if convicted by the US tribunal in Cuba. Correspondents say the hearing raises questions about military commissions.
The BBC's Jonathan Beale, one of 60 international journalists at the hearing, said it was the first time Khalid Sheikh Mohammed had been seen in public since his capture.
He said his appearance had changed dramatically since a photograph at the time of his arrest showing him dishevelled and unshaven.
The five defendants were all dressed in white, traditional Arab dress. Only defendant Ramzi Binalshibh was shackled.
Marine Col Ralph Kohlmann, presiding over the hearing, told Khalid Sheikh Mohammed he faced the death sentence if convicted.
"That is what I want, I'm looking to be a martyr for long time," Khalid Sheikh Mohammed replied.
Our correspondent says the alleged terror mastermind started singing an Arabic prayer, translated into English as "God is all sufficient".
Despite a warning from the judge against representing himself, Khalid Sheikh Mohammed said he could not accept any attorney "who was part of the evil US constitution".
The US describes Khalid Sheikh Mohammed, believed to have been al-Qaeda's third in command, as "one of history's most infamous terrorists".
Mr Binalshibh is a Yemeni man described by the US as the co-ordinator of the 9/11 attacks, who, according to intelligence officials, was supposed to be one of the hijackers, but was unable to get a US visa
He also told the court he wished to be "martyred".
"I have been seeking martyrdom for five years," he said.
Following his arrest he was held at a CIA secret prison, where he was subjected to harsh interrogation techniques and a practice known as waterboarding, that simulates drowning, until he was moved to Guantanamo Bay two years ago.
The US military says that as well as admitting involvement in the 11 September 2001 attacks on Washington and New York, he has confessed to being involved in more than 30 terrorist plots around the world, including plans to attack London's Big Ben and Canary Wharf.
Appearing alongside Khalid Sheikh Mohammed and Mr Binalshibh are:
- Mustafa Ahmad al-Hawsawi, a Saudi man said by US intelligence officials to be one of two key financial people used by Khalid Sheikh Mohammed to arrange the funding for the 11 September hijackings
- Ali Abd al-Aziz Ali, also known as Amar al-Balochi, who is accused of serving as a key lieutenant to Khalid Sheikh Mohammed - his uncle - during the 11 September plot
- Walid Bin Attash, a Yemeni national who, according to the Pentagon, has admitted masterminding the bombing of the American destroyer, USS Cole, in Yemen in 2000, which killed 17 sailors, and is who is accused of involvement in the 11 September 2001 attacks
The charges against them list "169 overt acts allegedly committed by the defendants in furtherance of the September 11 events".
The charges, which include 2,973 individual counts of murder - one for each person killed in the 9/11 attacks - are the first directly related to the 9/11 attacks to be brought against any Guantanamo inmates.
The five are among 19 prisoners due to face the military tribunals, which were set up in the wake of 9/11 to try non-US prisoners who have been classed as "enemy combatants" by the White House and therefore deemed to not be entitled to the legal rights normally afforded to prisoners.
Justice in the dock
The trials have already raised questions about not just the treatment of detainees, but also the legitimacy of American military commissions.
The US authorities say they have bent over backwards to make sure that the trials are fair but some of its own lawyers have already condemned the process as fundamentally flawed.
The trials are taking place in Camp Justice, a complex set up on the base
Human Rights Watch, a New York-based organisation, says the system lacks credibility given much of the evidence had been obtained through harsh interrogation techniques.
Later this month, the US Supreme Court is to rule on the rights of prisoners being held at Guantanamo Bay, threatening a possible delay or even halt to the proceedings.
The court ruled in 2006 that an earlier tribunal system was unconstitutional.