Washington (CNN) -- The long legal saga of convicted terrorist and 9/11 co-conspirator Zacarias Moussaoui may be now be over.
The imprisoned French native allowed a deadline for Supreme Court review of his case to lapse. That all but eliminated any further substantive appeals over his prosecution and life sentence.
Moussaoui had agreed to plead guilty in 2005 to six criminal conspiracy charges arising from the al Qaeda terror plot to use commercial aircraft to strike key U.S. targets on September 11, 2001, in the worst domestic terror attack in American history.
A three-judge panel of the U.S. Court of Appeals for the 4th Circuit earlier this year concluded Moussaoui's trial was fair, despite the defendant representing himself against the advice of the trial judge and his own lawyers. And the judges said a life sentence imposed by the jury was appropriate.
In a filing released this week, Moussaoui's court-appointed lawyers said their client "did not authorize" a petition to be filed with the high court, despite a letter advising him of that right.
Given that refusal, the seven appellate attorneys then asked to be relieved of their duties. The appeals court Tuesday agreed, in a one-sentence order.
In a final move, the legal team asked the appeals court to notify Moussaoui he had one last legal option, to file a petition for habeas corpus, further challenging his imprisonment. Such a step would be a distinct long shot and would have to be done with a new set of lawyers, or by himself if he so chose. The deadline to file that appeal is July 30, 2011.
Moussaoui has been held by the government since August 2001, and was the first person charged in the United States in connection with the 9/11 attacks.
He was indicted in December 2001, accused of being part of a broader terror conspiracy in the months leading up to 9/11. Several other accused top al Qaeda officials -- including alleged 9/11 mastermind Khalid Sheikh Mohammed -- are awaiting transfer into federal custody and prosecution in civilian courts, as was the case with Moussaoui.
Government sources have told CNN that three top al Qaeda detainees have told their interrogators that Moussaoui was not meant for the 9/11 plot, but for a future terror operation. Moussaoui had said as much in open court, admitting allegiance to al Qaeda leader Osama bin Laden, but denying he was to have been part in the 9/11 hijacking of planes. Prosecutors had questioned the validity of some of his claims.
The 41-year-old faced the death penalty, but was instead given life in prison, and serves his sentence at the "supermax" correctional facility in Colorado.
His trial had been delayed for many months over the question of whether the French citizen of Moroccan descent had the right to introduce testimony from the three top al Qaeda leaders who he said may have evidence that could clear him. The
court had agreed but said no direct access was allowed, only written summaries of the interrogations. That evidence was the key basis of Moussaoui's current appeal.
"We find it significant that Moussaoui never sought to rescind the admissions he had just made" in his March 2005 guilty plea, wrote the judges in their January ruling denying his appeal, "nor to withdraw his guilty plea during the nearly three-year-long period that elapsed between his (initial) appeal and the conclusion of the sentencing proceeding."
Moussaoui tried to use bin Laden's own words to help his case. The Saudi leader -- reportedly in hiding in Pakistan or Afghanistan -- said in an audio message, "I was responsible for entrusting the 19 brothers -- Allah have mercy upon them --- with those raids ... and I did not assign brother Zacarias to be with them on that mission." Those 19 Muslim men were the al Qaeda members aboard the planes that crashed on 9/11.
At the same time, the defendant also claimed he was supposed to fly a fifth plane into the White House, and that Richard Reid, known as the "shoe bomber" because of his attempt to ignite explosives hidden in his shoe on a commercial airplane flight, was supposed to be on his hijacking team. Only four planes were involved in the 9/11 attacks.
But after his May 2006 sentencing, Moussaoui claimed he lied on the stand. His erratic behavior at trial -- including his frequent outbursts and threats, and his insistence of representing himself for a time -- led to calls for a mistrial by his legal team.
In his last public appearance at his sentencing, Moussaoui waved the "V" victory sign, and attacked the United States. "We will come back another day," Moussaoui told the court. "As long as you don't hear, America, you will feel ... God curse
America. God bless Osama bin Laden. You will never get him."
The Supreme Court had earlier refused to stop his trial from going ahead.
The case is Moussaoui v. U.S. (06-4494).