A federal judge will accept a guilty plea from the man once believed to be the "20th hijacker" in the Sept. 11, 2001, attacks (search) on Friday.

A hearing to accept a guilty plea in U.S. v. Zacarias Moussaoui (search) is scheduled for Friday at 3:30 p.m. EDT at the Albert V. Bryan United States district Courthouse in Alexandria, Va. U.S. District Judge Leonie M. Brinkema (search) will preside over the proceedings.

If Brinkema accepts a plea, she would then probably set a death penalty trial, at which jurors would decide if Moussaoui should be executed.

The government accused Moussaoui of participating in an Al Qaeda (search) conspiracy to commit terrorism that included the 2001 attacks on the World Trade Center in New York and the Pentagon in Washington that left nearly 3,000 people dead.

Click here for the Moussaoui case history (FindLaw).

Moussaoui has only confessed to being a member of Al Qaeda and pledging his loyalty to Usama bin Laden. Court observers believe that alone could be enough to send him to jail for the rest of his life.

At this time, there is no evidence of any sort of "deal." Moussaoui is seeking to enter the plea against his lawyers' advice. Presumably he will plead to what he has been charged with -- conspiracy in the Sept. 11 attacks. There is no evidence at this point that the prosecution has any part in this decision or is expecting any "information" in return. The prosecution will likely still pursue the death penalty against him.

A closed hearing was held Wednesday to determine whether Moussaoui "understands the ramifications of entering a guilty plea in his role in the plot. It was at that hearing that Brinkema scheduled the Friday proceeding.

Brinkema on Wednesday ruled that Moussaoui "is fully competent to plead guilty to the indictment."

On the point of Moussaoui's mental competency, his lawyers have long said they feel he is not competent. They may file court papers Wednesday or Thursday to that effect.

Moussaoui, 36, recently wrote a one-page letter to the judge and federal prosecutors in which he said he wants to plead guilty; it was sent from his jail cell two weeks ago. One source told FOX News that his wish to enter the plea and likely face the death penalty are against the advice of his attorneys. Sources told The Los Angeles Times that Moussaoui's lawyers wanted his request actually thrown out, arguing that it's his naive attempt to win a hearing before the U.S. Supreme Court.

But the high court last month declined to hear Moussaoui's appeal and it let stand a 4th U.S. Circuit Court of Appeals ruling that kept the death penalty in play and ordered a compromise on Moussaoui's access to top-ranking Al Qaeda figures that are in U.S. custody.

Moussaoui tried to plead guilty in 2002 by claiming he knew intricate details of the plane hijackings. But he rescinded his plea a week later. His mental state has been an issue in the case ever since.

Moussaoui was indicted on six charges in December 2001, but his trial has been delayed three times. Four of those charges are considered "death penalty" offenses. The charges are: conspiracy to commit acts of terrorism, conspiracy to commit aircraft piracy, conspiracy to destroy aircraft, conspiracy to use weapons of mass destruction, conspiracy to murder U.S. employees and conspiracy to destroy property.

Eliminating a trial would spare Brinkema from working with prosecutors and defense lawyers to craft unclassified summaries of statements by the three Al Qaeda prisoners -- the compromise courts created to allow Moussaoui some access to their testimony.

In his handwritten filings, Moussaoui has railed against the U.S. government, Brinkema and his lawyers. In 2003, Brinkema stripped him of his right to defend himself, saying his legal filings "include contemptuous language that would never be tolerated from an attorney and will no longer be tolerated from this defendant."

In one of his last filings before the judge revoked his right to defend himself, Moussaoui said he wanted "anthrax for Jew sympathizer only," called then-Attorney General John Ashcroft, who is a Republican, "the Democratic Jerk" and referred to Brinkema as "Leonie you Despotically Judge."

The government has long believed that 20 people were meant to hijack the four jetliners on Sept. 11, although only 19 boarded the planes that morning. Moussaoui was first thought to be the possible 20th hijacker but prosecutors, along with the independent government commission that investigated the attacks, have dropped his name as the possible 20th person involved.

They now suggest that the Sept. 11 planners believed him too unstable to join the hijackers.

Moussaoui was arrested in August 2001 after a flight instructor in Minnesota alerted the FBI to what appeared to be suspicious behavior. He was in federal custody on immigration charges when the attacks occurred; he was indicted after the attacks.

His case is the only one related to the attacks that has come close to going to trial, and the Bush administration has viewed it as a key prize in its War on Terror, although it's been far from the slam-dunk case as originally anticipated.

FOX News' Catherine Herridge and Anna Persky and The Associated Press contributed to this report.