There are many conspiracy theories that attribute the planning and execution of the September 11 attacks against the United States to parties other than, or in addition to, al-Qaeda[1] including that there was advance knowledge of the attacks among high-level government officials. Government investigations and independent reviews have rejected these theories.[2][3] Proponents of these theories assert that there are inconsistencies in the commonly accepted version, or evidence that was either ignored or overlooked.[4]