is so far the only person to be charged in the United States in
connection with the 11 September attacks. BBC News Online answers
key questions about his trial.
What is Moussaoui charged
Zacarias Moussaoui, a 35-year-old French citizen of Moroccan
origin, is the only person so far charged in connection with the 11
September attacks on America.
The US Government regards Mr Moussaoui as the "20th hijacker" -
and accuses him of conspiring with the 19 other men alleged to have
carried out the attacks on New York and Washington.
Mr Moussaoui was arrested on immigration charges three weeks
before the suicide hijackings after he aroused suspicions at a
flight school in Minnesota.
He is charged on four counts that carry the death penalty in the
case of conviction - conspiracy to commit acts of terrorism, to
commit aircraft piracy, to destroy aircraft and to use weapons of
He is also charged with conspiracy to kill US Government
officials and destroy US Government property - two lesser charges.
How strong is the evidence
Prosecutors have said that Mr Moussaoui's actions mirror those of
the 19 alleged hijackers behind the 11 September attacks.
He went through flight instruction, is alleged to have received
money from a terrorist suspect and is alleged to have been trained
at an al-Qaeda camp.
The US authorities have not offered evidence of a direct link
between him and the hijackings.
Some legal experts have said that the evidence against Mr
Moussaoui is circumstantial and that there is only evidence of
association with some of those who are alleged to have carried out
He has said in court that he provided a guest house for al-Qaeda
members, but insisted that he was not involved in the attacks.
Why did Moussaoui plead
guilty and then withdraw his plea?
Mr Moussaoui pleaded guilty to some of the charges against him in
July 2002, but then changed his mind and withdrew the plea.
The hearing judge rejected that plea, ordering him to take a week
to consider his decision.
At one court appearance, Mr Moussaoui said he was a member of
al-Qaeda and had sworn a pledge of allegiance to Osama Bin Laden.
It is not exactly clear why Mr Moussaoui entered and then
reversed his plea. One suggestion is that he did not understand the
gravity of his situation and the charges against him.
Another theory is that he wanted to short-circuit a long jury
trial that he felt would inflame public opinion against him.
Is Moussaoui fit to stand
There have been questions about Mr Moussaoui's state of mind, and
his fitness to stand trial.
His behaviour in court has been erratic and at times he has not
appeared to understand what is happening to him - specifically the
seriousness of the charges against him.
He has insisted on representing himself, accusing his
court-appointed lawyers of trying to kill him.
As the only person charged by the US Government in connection
with the 11 September attacks, he is under tremendous pressure that
is only increased by this isolation.
The judge in the case has ruled that he is mentally fit to stand
Could the case end up before
a military tribunal?
Yes, because of a dispute over whether an alleged al-Qaeda
leader, Ramzi Binalshibh, should be allowed to testify before the
Prosecutors say Mr Moussaoui received funds from Mr Binalshibh,
who allegedly helped finance the 11 September attacks.
Mr Moussaoui's lawyers have always disputed this. When Mr
Binalshibh was arrested in Pakistan in September 2002, they
requested permission to interview him, saying his deposition was
crucial in proving their clients' innocence.
The Virginia judge handling the case, Leonie Brinkema, has agreed
in principle to an interview over closed-circuit television.
The decision has infuriated prosecutors. They object to any such
move on security grounds, and have filed an appeal.
The US Justice Department has so far been keen to try Mr
Moussaoui in an open court, where the unanimous verdict required for
a conviction would carry weight.
But the administration could change its mind it views a public
trial as a threat to national security.
If it forced to allow Mr Binalshibh to testify, the option of a
closed military tribunal - where only a two-thirds majority is
required for a verdict - remains available to the US Government.