After more than six weeks of prosecutors and defense lawyers arguing before a jury over whether Moussaoui should be put to death, on May 3 the jury finally reached its decision.
"In the case of the United States versus Zacarias Moussaoui, as to count one, conspiracy to commit acts of terrorism transcending national boundaries, and count three, conspiracy to destroy aircraft, and count four, conspiracy to use weapons of mass destruction, the jury has found the defendant should be sentenced to life in prison without the possibility of release," U.S. federal court spokesman Edward Adams told journalists outside the courthouse in Alexandria, Virginia, near Washington, D.C.
The decision was a defeat for the prosecution, which had argued that Moussaoui deserved execution because he was directly responsible for the nearly 3,000 deaths in the September 11 attacks.
Just three weeks before the attacks, Moussaoui was arrested on immigration charges at a school where he was learning to fly in the Midwest. The prosecution argued that he deliberately lied to police at that time to hide the plot and allow it to go forward.
But defense attorneys argued that even if Moussaoui had not lied, there was no certainty that investigators at the time would have acted on any information he provided. That is because, the defense argued, investigators ignored other warning signs before the attacks.
In the jury debate, several jurors favored the death penalty for Moussaoui. But the jury of nine men and three women was unable to reach a unanimous decision to execute him, and opted for life imprisonment instead.
After the May 3 verdict, both the defense and prosecution said they believed justice was done. Gerald Zerkin, a court-appointed defense lawyer for Zacarias, told journalists outside the court that the jury had correctly weighed Moussaoui's role in the attacks.
"By listening to the result, it's obvious that [the jurors] thought that [Moussaoui's] knowledge of 9/11, his role of 9/11, was not very great and that that played a significant role in the result that we had," Zerkin said.
Speaking for the prosecution, U.S. Deputy Attorney General Paul McNulty said that even without a death sentence, Moussaoui had been made accountable for his acts. "Accountability for the crimes committed has been achieved through the prosecution," he said. "There is no doubt about that."
It is unclear how Moussaoui himself regards the sentence. During the trial, there was much media speculation that Moussaoui wanted execution to fulfill his own visions of martyrdom. He often refused to cooperate with his defense lawyers and showed contempt for their efforts.
However, as the verdict of life imprisonment was read out today, Moussaoui shouted to the courtroom: "America, you lost! I won!"
Civil Terrorism Trial
Moussaoui, a 37-year-old French citizen of Moroccan descent, is the only person to have been tried in a court in the United States in connection with the September 11 attacks. His on-again, off-again court process lasted four years.
Claiming to act on direct orders from Al-Qaeda chief Osama bin Laden, Moussaoui was tried in a U.S. civil court at the insistence of the Justice Department.
That is despite the fact that much of the U.S.-led war on terrorism involves bringing suspects held in Guantanamo Bay, Cuba, or Afghanistan before military tribunals.
Some 35 members of the families of September 11 victims testified during the arguments over whether Moussaoui deserved the death penalty. Those arguments ranged widely, including whether Moussaoui was himself a victim of a troubled childhood that made him schizophrenic and delusional.
Moussaoui will now spend the rest of his life at a maximum-security prison in Colorado. He has previously said that he has "no regret, no remorse" and wished every day could be September 11, 2001.