Zacarias Moussaoui's guilty plea in the Sept. 11 terrorist attacks was invalid because the government failed to turn over evidence that could have helped his defense, his attorney told a federal appeals court Monday.

Justin Antonipillai urged a three-judge panel of the 4th U.S. Circuit Court of Appeals to throw out the plea and order a new trial for Moussaoui, who once claimed to be part of the 2001 conspiracy but has since changed his story. Moussaoui was sentenced to life in prison.

U.S. Justice Department attorney Kevin Gingras argued that Moussaoui, the only person to stand trial in a U.S. court in the 9/11 attacks, knew the trial judge was considering ways to get the favorable evidence to him but decided to plead guilty anyway.

"It was his choice to pull the plug on the process," said Gingras. The prosecutor said U.S. District Judge Leonie Brinkema "bent over backward" to ensure that Moussaoui understood what he was doing and the consequences.

The panel peppered both attorneys with questions for 90 minutes before closing the hearing for about an hour to consider matters involving classified information.

The court usually takes several weeks, or even months, to issue a decision.

In open court, Chief Judge Karen J. Williams sounded skeptical of Antonipillai's claim that Moussaoui's trial preparations were impaired by government secrecy that some of his constitutional rights were violated.

Williams wondered aloud how the court could conclude that the government would have continued to conceal the evidence had the case gone to trial. She also noted Moussaoui testified that he was supposed to hijack a fifth plane and crash it into the White House.

Antonipillai said Moussaoui had "delusions of grandeur," and his confession was contradicted by alleged 9/11 ringleader Khalid Sheikh Mohammed, who said Moussaoui was training for a different operation and had nothing to do with the terrorist attacks that killed nearly 3,000 people.