ALEXANDRIA, VIRGINIA - Federal prosecutors argued yesterday that even though September 11 conspirator Zacarias Moussaoui was in jail during the attacks he should be executed because his lies led to the deaths of 3,000 people.

But one of his court-appointed lawyers said executing Moussaoui would only make him a martyr because many al Qaeda members only "live so that they can die."

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.

"Please don't make him a hero," defence attorney Edward MacMahon said at the start of the trial to determine Moussaoui's sentence. "He just doesn't deserve it."

Moussaoui, 37, was arrested the month before the 2001 attacks after raising suspicions at a flight school. Prosecutors said the hijackings might have been averted if he had not lied to investigators and told them what he knew.

"Even though he was in jail on September 11, 2001, Moussaoui did his part ... as a loyal al Qaeda soldier," said lead prosecutor Robert Spencer. "His lies provided the operational security and allowed his brothers to go forward and kill."

"Had Moussaoui just told the truth on September 11, 2001, it would all have been different," he said

Moussaoui, dressed in a green prisoner's jumpsuit and a white cap, spent most of his time leaning back in his chair rubbing his long, bushy beard. In the past he has disrupted court appearances, but this time he watched with little expression and took notes.

But when the government later showed two videotapes -- one of Osama bin Laden and another depicting an al Qaeda training camp -- Moussaoui smiled and mouthed the words to some songs.

After the judge left the courtroom, Moussaoui criticised MacMahon -- one of several court-appointed attorneys whom Moussaoui detests -- and vowed to testify to tell his side of the story.

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 hijackings.

The jury must first decide whether his actions led directly to at least one death on Sept 11. If it decides that they do, another phase of the trial will be held to decide if Moussaoui will be executed. If the jury finds the opposite, he would receive life in prison.

MacMahon called the government's argument "entirely speculative."

"The evidence in this case will be entirely clear that Moussaoui was totally uninvolved in the 9/11 plot," he said.

"This trial cannot be viewed by you as jurors as part of the war on terror," MacMahon added. "We must give this man a fair trial no matter who he is, what he thinks of us and who he represents."

A few relatives of those who died on September 11 were in the courtroom and others watched at special viewing rooms in Boston, New York, New Jersey, Philadelphia and at the Alexandria courthouse.

At the Manhattan courthouse, Barry Zelman, 51, wearing a large badge with a picture of his brother who died in the World Trade Centre, said it will be hard watching the trial.

"There's going to be a lot of anger and a lot of emotion," Zelman said. "He's al Qaeda in the flesh."

"For most of us I hope it brings some peace and healing," said Eunice Hanson, who lost her son, daughter-in-law and granddaughter on one of the planes that struck the trade centre. "It will be painful, very painful."

The charges against Moussaoui were conspiracy to commit acts of terrorism, commit aircraft piracy, destroy aircraft, use weapons of mass destruction, murder US employees and destroy property.

Although he claims he was not meant to be part of the September 11 attacks, he said Osama bin Laden had picked him to fly a plane into the White House as part of a broader conspiracy.