US Edition In an abrupt reversal of previous attempts to defend themselves, Khalid Sheikh Mohammed and his four co-defendants indicated to a judge in Guantánamo Bay they want to plead guilty.
The move is being seen as an apparent attempt to push through their prosecution and execution for multiple murder charges.
Their admission that they took the decision on November 4, the day on which Barack Obama won the US presidency, provided the strongest clue as to their motives. Mr Obama has said he wants to close down the controversial detention camp and try its inmates elsewhere.
Relatives of some of the victims, allowed to watch a 9/11 hearing for the first time, sat at the back of a courtroom on the US military base as the accused passed a note to the military judge.
They said they had "reached an agreement to request from the commission an immediate hearing session in order to announce our confessions... with our earnest desire in this regard without being under any kind of pressure, threat, intimidations or promise from any party".
The letter did not implicitly say they intended to plead guilty to the 2,973 murder counts – one for each person killed after al Qaeda militants hijacked three airliners in 2001. However each of the five told the judge they were prepared to enter a plea.
The five have previously said they would welcome 'martyrdom', a fate they might be denied by the Obama administration unless they hurry along the legal process.
The judge, Colonel Steven Henley of the US Army, questioned the five – who face the death penalty – on their decision to ensure they understood its impact.
Mohammed, a Kuwait-born Pakistani, and four others – Ramzi Binalshibh, Mustafa Ahmed al Hawsawi, Walid bin Attash and Ali Abdul Aziz Ali – were charged earlier this year with conspiring with al Qaeda to kill civilians.
Mohammed has already boasted that he planned the attacks "from A to Z".
He told the judge yesterday he had no faith in either him, his defence lawyers or in President Bush.
Speaking in English, his grey beard stretching down to his chest, he told the court: "I am not trusting any Americans".
The five said they withdrew all previous motions that had been filed by their Pentagon-appointed lawyers, whom they have attempted to sack.
Amid uncertainty as to whether a military judge can actually accept a guilty plea in a capital case, Col Henley said he would have to hold further hearings on the issue.
He will also have to decide whether the five's incarceration and torture affected their judgment.
It is the fourth time the defendants have appeared before a tribunal judge at Guantánamo and legal experts believe there is little chance the case will be ready for trial before Mr Obama takes office on January 20.
"The last thing this country needs is a rush to execution," said Jennifer Daskal, senior counter-terrorism counsel at the campaign group Human Rights Watch, who was in the courtroom.
"Any verdict or decision in 9/11 cases ought to be a major victory for US justice. Holding these defendants accountable for terrible crimes has been tainted by torture and an unfair military commissions process."
Nine relatives of victims of the 9/11 attacks, chosen by lottery from 100 applicants, were invited to watch the legal proceedings.
Alice Hoagland, a Californian whose son, Mark Bingham, died in the United plane that crashed in a Pennsylvania field, said the announcement was "like a real bombshell to me".
She told reporters that Mr Obama was an "even-minded and just man" who would ensure the five were punished.