Moussaoui was sentenced to life in prison after pleading guilty to helping plan the 2001 terrorist attacks. His lawyers now claim court-imposed secrecy undermined Moussaoui's ability to present an adequate defense, so the plea should be thrown out and a new trial granted.

A three-judge panel of the 4th U.S. Court of Appeals will conduct Monday's hearing in two parts. They'll meet in open court and then close the hearing for matters involving classified information.