Nineteen hijackers took thousands of innocent victims with them when they willfully crashed to their deaths September 11 — but federal investigators theorize there was supposed to be a 20th hijacker.

Zacarias Moussaoui, the first — and so far only — person charged directly in connection with the attacks, had been arrested only weeks before and was sitting in jail when the worst terrorist act on U.S. soil shook the nation.

Authorities say that Moussaoui was supposed to be on the plane they believe was headed for the White House before passengers overpowered the hijackers and the plane crashed into a Pennsylvania field. There were four hijackers on board that plane — but there were five on each of the three aircraft that hit the World Trade towers and the Pentagon.

Now the man who the government believes was supposed to be on a suicide mission is facing the death penalty.

Though Moussaoui's trial is slated to begin in the fall in Alexandria, Va., the case has already been filled with plenty of drama — from the controversy surrounding a bid to televise the trial to the defendant's handwritten motions denouncing the United States, Jews and even his trial judge.

Armed with a 31-page indictment that details the activities of Moussaoui and the 19 hijackers, federal prosecutors say Moussaoui was taking flying lessons in the months leading up to the attacks and is connected to known terrorists and Muslim extremists.

Moussaoui claims that he is innocent — and even contends that "concrete and direct proof" of his innocence is in the possession of the FBI. In June, the French citizen of Moroccan descent won the right to represent himself at trial.

Coming to America

Moussaoui arrived in the United States in February 2001 and immediately enrolled in an Oklahoma flight school. While there, according to the indictment, he inquired about crop dusting. And like the hijackers, Moussaoui joined a gym.

At the end of July, he received a two wire transfers totalling $15,000 from Ramzi Bin al-Shibh, whom government officials say wired money to some of the other hijackers and a flight school in Florida, according to the indictment. Prosecutors charge that Moussaoui received another transfer of $14,000 from Bin al-Shibh only a few days later.

Bin al Shibh — the former roommate of the man investigators say is the "ringleader" of the hijackers, Mohammed Atta — tried several times to gain entry to the United States himself and even applied to a flight school, but was denied a visa.

After spending five months and $6,000 on the course, Moussaoui was still unable to fly a plane alone. He dropped out and moved to Minnesota on August 10. A few days after his arrival, he paid $8,000 to enroll in Pan Am International Flying Academy in Eagan for a commercial flying course.

His instructors grew suspicious of their new student after he asked to use their Boeing flight simulators. According to some published reports, he even said that he didn't want to learn how to take off or land — only how to make turns — and asked questions about flying in New York.

School officials contacted the FBI several times before Moussaoui was arrested on a passport violation August 16 — 26 days before the attacks.

The Investigation

Following his arrest, authorities searched Moussaoui's home and found two knives, a manual for a Boeing 747; fighting gloves and shin guards and the name "Ahad Sabet" — one of the many aliases Bin al-Shibh goes by — written in a notebook.

But while they seized his laptop, they needed a warrant to view the information stored on the computer's hard drive. The warrant was denied based on Foreign Intelligence Surveillance Act, a civil liberties statute.

On August 26, French officials notified the FBI that they had been keeping a file on Moussaoui since 1994, and warned that he had ties to Al Qaeda organization and Osama bin Laden. The FBI and CIA reviewed the information, but concluded there was not enough evidence that he posed a security threat. He remained in the custody of the Immigration and Naturalization Service.

It wasn't until after the attacks that the FBI went into the computer to find a flight simulator computer program, software regarding the Boeing 747 and extensive information about crop dusters.

The issue continues to raise questions about the FBI's handling of the situation, and speculation that had more action been taken they would have had been better prepared to handle or even prevent the attacks.

On the three-month anniversary of the attacks, Moussaoui was indicted on six counts — conspiracy to commit acts of terrorism, murder and air piracy, to destroy aircraft and property, and to use weapons of mass destruction.

Since his indictment, investigators uncovered even more evidence linking Moussaoui to other terror suspects.

Moussaoui attended the same mosque in London as Richard Reid, an Islamic convert who is facing trial for allegedly trying to ignite his sneakers — which contained explosives — while on board a Miami-bound flight.

According to prosecutors, passengers stopped him before he set his feet ablaze and the plane made an emergency landing. A federal indictment charges that Reid was trained by Al Qaida, but Reid claims that he acted alone and that he learned to make bombs on the Internet.

Flying Solo

In numerous handwritten motions filed with the court, Moussaoui insists that his court-appointed defense lawyers were conspiring with the FBI and complains that "the United States is unfairly trying to kill me."

In the documents, he declares himself "a dedicated enemy of the United States of America," making derogatory statements about Jews and charging that Judge Leonie Brinkema, who will preside over his trial, is suffering from a mental disorder.

But Brinkema sided with Moussaoui when he made a motion to fire his lawyers and represent himself — a move some legal commentators feel will work against him in front of a jury. The order allowing him to represent himself was granted on the condition that he has an attorney acting as co-counsel. Moussaoui said he would seek the assistance of a Muslim-American lawyer. Brinkema also ordered that Moussaoui be given the use of a computer while in jail to help him prepare his defense.

While Moussaoui had voiced support for televising of the trial, television cameras are not allowed in federal courtrooms unless a judge signs a waiver. Though Court TV applied to televise the trial, the application was denied because of national security issues.

Jury selection is scheduled to begin Sept. 30.