Alexandria, Va. ? Hoping to put to death the only man charged in the 9-11 conspiracy, federal prosecutors opened the sentencing trial for terrorist Zacarias Moussaoui on Monday by disclosing that documents found in his possession after his arrest three weeks before the attacks linked him to the four men who piloted the hijacked jets.

Assistant U.S. Atty. Robert A. Spencer told the jury that if Moussaoui, who was being held on a visa infraction, had told FBI agents about phone calls he had made and two lists of U.S. flight schools he kept hidden in a duffel bag, the government could have prevented the deadliest terrorist operation in U.S. history.

“The FBI would have quickly been on to all four pilots of the hijacked planes,” Spencer said. “But Moussaoui lied so his brothers could go forward. He lied and nearly 3,000 people perished.”

But Moussaoui’s defense attorneys, in their own opening statement, said that while agents were highly suspicious of Moussaoui, they never formally sought or obtained a government search warrant to open his belongings in the first place.

Furthermore, the defense lawyers said, authorities knew that several hijackers were in the United States but, because of government infighting, never devoted the manpower to hunting them down.

One of the court-appointed lawyers, Edward B. MacMahon, characterized Moussaoui, a French citizen and self-admitted al-Qaida operative, as more of a dunce who was never taken seriously. He noted that after Moussaoui was arrested on Aug. 16, 2001, no one from the terror cell in this country or operatives abroad contacted him or came to his aid.

An Artist sketch of court proceedings for Zacarias Moussaoui in Alexandria, Va., Monday, March 6, 2006. Moussaoui is seen watching a videotape of Osama Bin Laden.

One al-Qaida operative later conceded that Moussaoui was considered “cuckoo in the head,” MacMahon said, and the terror organization gave him money at times “just to get rid of him.”

The lawyer further suggested that al-Qaida chieftains placed Moussaoui in the United States purposely to throw federal agents off the track of the real plot. “Moussaoui did not train with them because he was not on their team,” MacMahon said.

The 37-year-old Moussaoui, a Moroccan by descent who turned to radical Islamic fundamentalism in England, pleaded guilty in April to six criminal charges in the 9-11 conspiracy.

Three of the charges make him eligible for the death penalty. The jury will decide whether to sentence him to death, or to life in prison.

About 200 people from as far as Rhode Island and Connecticut joined New Yorkers in the Manhattan Federal Courthouse to see the opening of Moussaoui’s penalty trial. The families of other victims watched at courthouses in Central Islip, N.Y.; Boston; Newark, N.J.; and Philadelphia.

Many hoped to see Moussaoui squirm under the threat of a death penalty, but left tearful and angry that he simply slouched in his chair, stroking his beard and sipping water.