I didn't know either... just googled him : Moussaoui is said to have been a replacement for the "first" 20th hijacker, possibly Ramzi Binalshibh (bin al-Shibh), a member of the Hamburg cell. Binalshibh and Zakariyah Essabar were denied visas to the US, so the men allegedly scrambled to find another man to fill the spot. He followed a path similar to others known to have been involved, such as visiting terrorist training camps in the Middle East, purchasing knives while in the U.S., and attending some of the same flight schools. However, prosecutors in Moussaoui's drawn-out trial had difficulty directly connecting him to the 19 participants. He also saw the trial as an opportunity to have a soapbox to advertise Islamic fundamentalism and his views on America. He surprised onlookers by electing to represent himself in court, expressed contempt for the trial by introducing legal motions deriding Judge Leonie Brinkema, and rankled the federal prosecutors by requesting the presence of captured Al-Qaeda members as witnesses in his case. Moussaoui has admitted being a member of Al Qaeda.

During the trial, Moussaoui initially stated that he was not involved in the September 11 attacks, but that he was planning an attack of his own. He stated that this plan involved hijacking a Boeing 747-400 in order to free the blind sheikh Omar Abdel-Rahman, being held in Florence, Colorado, and return him to Afghanistan. Some Al-Qaeda members reportedly corroborated Moussaoui's statement to an extent, saying that he was involved in a plot other than September 11, but prosecutors believed that his story had no merit. On April 3, 2006, Moussaoui was found to be eligible for the death penalty. Before leaving the courtroom, he was reported to have shouted, "You will never get my blood. God curse you all!" [1]