US Federal prosecutors argued today that even though Zacarias Moussaoui was in jail during the 11 September 2001 attacks he should be executed because his lies led directly to the deaths of 3,000 people.
But one of his court-appointed lawyers said that executing Moussaoui would only make him a martyr.
Moussaoui, a French citizen of Moroccan descent, pleaded guilty in April to six counts, three of which carry the death penalty. The charges included conspiracy to commit terrorism.
The 37-year-old was arrested the month before the 2001 attacks after raising suspicions at a flight school. Prosecutors said if he had not lied to investigators and told what he knew, the hijackings might have been averted.
Dressed in a green prisoner's jumpsuit and a white cap, he spent most of his time leaning back in his chair rubbing his long, bushy beard. In the past he has disrupted some court appearances, but this time he watched and took notes with little expression.
Earlier, US District Judge Leonie Brinkema seated 12 jurors and five alternates in the only trial to be held in the United States in connection with the attacks, which killed about 3,000 people.
The jury must first decide whether his actions led directly to at least one death on 11 September. If the jury finds they did, he can be executed, but if they find the opposite he would receive life in prison.
Around 3,000 people were killed when teams of hijackers crashed two civilian airliners into the World Trade Center in New York and one into the Pentagon, while a fourth plane went down in a field in Pennsylvania, after passengers apparently fought back.
