A lawyer for Zacarias Moussaoui has told a federal appeals court in Virginia that the Sept. 11 conspirator is entitled to a new trial.

Moussaoui is serving a life sentence after pleading guilty to helping plan the 2001 terrorist attacks. But his lawyer told a three-judge panel Friday that the plea was unconstitutional because his trial lawyers had to undergo a national security background check, which restricted Moussaoui's right to choose counsel.

Moussaoui also claims he was denied helpful evidence. A federal prosecutor said Moussaoui decided to plead guilty before that evidence could be provided.

The 4th U.S. Circuit Court of Appeals first heard Moussaoui's appeal in January but ordered new arguments when a panel member retired before the case could be decided.