A jury of nine men and three women decided Zacarias Moussaoui's fate. (Canadian Press)

Moussaoui is a 37-year-old French citizen of Moroccan descent. He was actually in a U.S. jail at the time the four planes were hijacked on that fateful day. Moussaoui had come to the attention of the FBI three weeks earlier after arousing suspicion at a Minnesota flight training school. School staff said he seemed interested only in learning how to steer a jet, not in taking off or landing.

In April 2005, Moussaoui pleaded guilty to six charges relating to his involvement in the attacks, including conspiracy to commit acts of terrorism, conspiracy to use weapons of mass destruction and conspiracy to destroy aircraft.

He has been referred to as the "20th hijacker" – the other 19 were on board the jets that crashed into the twin towers of the World Trade Center in New York, the west wing of the Pentagon in Washington and a field near Pittsburgh, Penn.

During his trial, U.S. prosecutors said Moussaoui deserved the death penalty, saying he knew of the Sept. 11 plot and could have prevented it. Moussaoui himself claimed to have been a key al-Qaeda operative. He surprised everyone by saying he had been scheduled to hijack a fifth plane on Sept. 11 – along with convicted "shoe bomber" Richard Reid – and fly it into the White House. His defence lawyers said their client was mentally ill.

Moussaoui is sentenced to life in prison, with no possibility of parole. One vote spared Moussaoui from the death penalty, the jury foreman at his trial later tells the Washington Post.

Timeline:

May 23, 2006:
An audio tape purported to be made by Osama bin Laden is found on the internet and mentions Moussaoui: "The truth is that he has no connection whatsoever with the events of Sept. 11 … His confession that he was assigned to participate in those raids is a false confession … a result of the pressure put upon him for the past 4½ years."

May 12, 2006:
The jury foreman at Zacarias Moussaoui's trial said a single vote spared Moussaoui from the death penalty. The foreman spoke to the Washington Post, on the condition of anonymity. She said the jury voted 10-2, 10-2 and 11-1 in favour of the death penalty on the three charges for which Moussaoui was eligible for execution. A unanimous vote on any of the charges would have meant a death sentence for Moussaoui.
» CBC STORY: Single vote spared Moussaoui from death penalty, says report

May 8, 2006:
Moussaoui asks a federal judge to allow him to withdraw his guilty plea so he can be tried again, promising he won't lie on the witness stand this time. The judge immediately denies the request.

May 4, 2006:
Judge Leonie Brinkema refutes Moussaoui's boast that "America, you lost, I won!" after a jury decided to spare his life. "Mr. Moussaoui, you came here to be a martyr in a great big bang of glory," Brinkema says. "But to paraphrase the poet T.S. Eliot, instead you will die with a whimper."
» CBC STORY: 'It's absolutely clear who won,' judge tells Moussaoui

May 3, 2006:
A U.S. federal jury in Alexandra, Va., rejects the death penalty for Moussaoui and decides he must spend the rest of his life in prison without the possibility of parole.
» CBC STORY: Zacarias Moussaoui sentenced to life in prison

April 28, 2006:
During the sentencing deliberations, a juror uses a computer in the jury room to look up the word "aggravating" on an online dictionary. The judge admonishes the juror for using "extraneous evidence," but decides the deliberations can continue.
» CBC STORY: Judge scolds Moussaoui juror for using online dictionary

April 24, 2006:
A jury begins deliberating Moussaoui's sentence. Before they were sequestered, the prosecution urged the jurors to "put an end to his hatred and venom," while Moussaoui's defence asked for life in prison, saying it would be "the long, slow death of a common criminal."
» CBC STORY: Jury deliberating on Moussaoui's fate

April 12, 2006:
The cockpit voice recording of the final 31 minutes of Flight 93, which crashed in a field in Pennsylvania on Sept. 11, 2001, is played for jurors. The audio is not released for media use, but the transcript is made public.
» CBC STORY: Last moments of doomed Flight 93 heard on tape

April 3, 2006:
After hearing four weeks of testimony, a U.S. federal jury decides Moussaoui is eligible for the death penalty.
» CBC STORY: Jury declares Moussaoui candidate for death penalty

March 27, 2006:
During his sentencing hearing, Moussaoui claims that he and another al-Qaeda member were scheduled to fly a fifth hijacked jet into the White House on the morning of Sept. 11, 2001.
» CBC STORY: 9/11 plot included attack on White House: Moussaoui

March 6, 2006:
Moussaoui's sentencing trial begins in Alexandria, Va.
» CBC STORY: Moussaoui blamed for 3,000 deaths in Sept. 11 attacks

Feb. 6, 2006:
Jury selection begins in the sentencing trial of Moussaoui. During the selection, Moussaoui shouts, "I am al-Qaeda" and "This trial is a circus." He is escorted from the courtroom by federal marshals.
» CBC STORY: Moussaoui disrupts jury selection with shouts

April 22, 2005:
Lawyers for Moussaoui file a motion in court arguing their client is incompetent to stand trial. However, Moussaoui says in court he understands he could be put to death for his role in planning attacks on the U.S. He then pleads guilty to all charges against him in connection with the Sept. 11 attacks on the United States.
» CBC STORY: Moussaoui pleads guilty

March 21, 2005:
The U.S. Supreme Court refuses to hear an appeal by Moussaoui's lawyers, challenging the government's right to try him without allowing direct questioning of al-Qaeda leaders in custody.

April 22, 2004:
A federal Appeal Court reinstates the death penalty as a possible sentence for Moussaoui.

April 2002 - November 2003
During this period, Moussaoui represents himself in his trial on six charges related to the Sept. 11, 2001, attacks. The period is marked by pleas offered and withdrawn, delays, postponements and Moussaoui's rants in court.
» CBC STORY: Lawyers try to block Moussaoui guilty plea

March 28, 2002:
Prosecutors announce that they will seek the death penalty.

Jan. 2, 2002:
Moussaoui refuses to enter a plea in his trial. The presiding judge enters a plea of not guilty on his behalf.
» CBC STORY: Judge enters not-guilty plea for Moussaoui

Dec. 11, 2001:
Moussaoui is charged with six conspiracy counts related to the Sept. 11 attacks. The six charges are:

• Conspiracy to commit acts of terrorism transcending national boundaries.
• Conspiracy to commit aircraft piracy.
• Conspiracy to use weapons of mass destruction.
• Conspiracy to destroy aircraft.
• Conspiracy to murder U.S. employees.
• Conspiracy to destroy property.

Sept. 11, 2001:
Moussaoui is moved to New York and held as a material witness in the investigation into the Sept. 11 attacks.

Aug. 17, 2001:
Moussaoui is arrested on immigration charges after arousing suspicion at a Minnesota flight school. Staff there said he asked to learn to fly a Boeing 747 and seemed interested only in learning how to steer a jet, not in taking off or landing.

Feb. 26 - May 29, 2001:
Moussaoui received training at a flight school in Norman, Okla., but doesn't get a pilot's licence.