Lawyers for Zacarias Moussaoui (search) on Thursday asked a U.S. appellate court to rule out the death penalty for the nation's only Sept. 11 defendant.

With restrictions imposed on Moussaoui's access to Al Qaeda (search) witnesses, the death penalty would be a cruel and unusual punishment in violation of the Constitution, the lawyers told the 4th U.S. Circuit Court of Appeals in Richmond, Va.

The government has vowed to seek Moussaoui's execution if he's convicted of participating in a terrorism conspiracy, along with the 19 terrorists who attacked the nation on Sept. 11, 2001.

The death penalty has been in and out of the case, which has lingered in the pretrial stage since late 2001.

The trial judge, reacting to the government's refusal to obey her orders on access to witnesses, had eliminated the possibility of imposing the death penalty.

Last month, a three-judge panel of the 4th Circuit said the penalty was too severe. It restored the prosecution's right to seek Moussaoui's execution.

The defense's written appeal to the full court was classified, although an edited version is expected to be made public.

Edward MacMahon Jr. (search), one of Moussaoui's lawyers, told The Associated Press in an interview that the key issue was the three-judge panel's rejection of Moussaoui's request to interview three Al Qaeda prisoners who may aid his defense. The interview was to have taken place through a remove video connection.

Moussaoui, a former Norman, Okla., resident, asserted the witnesses could testify that he did not have a role in the Sept. 11 conspiracy, although he was to participate in a subsequent Al Qaeda operation.

While the appeals panel denied the direct interview, it agreed with Moussaoui that he had the constitutional right to potentially favorable information, and ordered the trial judge to craft written summaries of statements the prisoners made to interrogators.

"If the government is going to restrict his ability defend himself, it should lose the option to seek his execution," MacMahon said. "Given the fact that the government doesn't have to produce the witnesses, we don't believe this should be a death penalty case."

The Eighth Amendment to the Constitution states: "Excessive bail shall not be required, nor excessive fines imposed, nor cruel and unusual punishments inflicted."

MacMahon also said the panel's ruling would allow the trial judge to have conflicting roles. U.S. District Judge Leonie Brinkema would approve the summaries the jury would see, thereby influencing Moussaoui's ability to defend himself, and make a ruling on whether the death penalty should apply.

The Moussaoui lawyers asked the full court to adopt the position of Judge Roger Gregory, who commented in a dissent that the ultimate penalty was unfair if Moussaoui couldn't have full access to the witnesses.