Excerpts from Books and Wikipedia
"Carried out by a group of Muslims inspired by the Islamic terrorist organization Al-Qaeda, the extremists killed about 3000 innocent victims. On the morning of September 11, four teams of terrorists, each with its own trained pilot, hijacked four planes bound for California from different airports. . . . In 1998, bin Laden issued an order for his followers 'to kill Americans everywhere.'" [Furtado: 1001 Days]