in advance the number of casualties from the enemy, who would be killed based on the position of the tower. We calculated that the floors that would be hit would be three or four floors. I was the most optimistic of them all ... We had notification since the previous Thursday that the event would take place that day. We had finished our work that day and had the radio on ... Muhammad [Atta] from the Egyptian family [meaning the al-Qaeda Egyptian group], was in charge of the group ... The brothers, who conducted the operation, all they knew was that they have a martyrdom operation and we asked each of them to go to America but they didn't know anything about the operation, not even one letter. But they were trained and we did not reveal the operation to them until they are there and just before they boarded the planes. In May 2002, FBI Director Robert Mueller noted that his organization had not uncovered a single piece of paper, "either here in the U.S. or in the treasure trove of information that has turned up in Afghanistan and elsewhere", that mentioned any aspect of the September 11 plot. In late November 2002, a letter attributed to bin Laden and translated by British Islamists surfaced, often called bin Laden's "letter to America". It states the motive behind the September 11 attacks as being: "because you attacked us and continue to attack us" and justifies the selection of a civilian target. Itemizing a list of perceived Western wrongdoings, the letter concludes that "the oppressed have a right to return the aggression" and hinted at further attacks. Also included are a list of demands, advice, and a statement of grievances against the American government and its people. On February 11, 2003, Al Jazeera broadcast an audio tape purportedly from bin Laden. Shortly before the US presidential election in 2004, in a taped statement, bin Laden publicly acknowledged al-Qaeda's involvement in the attacks on the US, and claimed a direct link to the attacks. He said that the attacks were carried out because "we are a free people who do not accept injustice, and we want to regain the freedom of our nation." In an audio message that surfaced on the Internet in May 2006, the speaker, who is alleged to be Osama bin Laden, defends Zacarias Moussaoui, who was undergoing a