Osama bin Laden plotted with al-Zawahiri, his number two, to carry out the violent attacks in the US along with six other men in Afghanistan. Five currently remain in Guantanamo Bay.
Of the 19 hijackers who took over the commercial aircrafts and crashed into the Twin Towers on September 11, 2001, 15 were Saudi nationals. The nation denies any involvement in 9/11.