After Atta was chosen as the leader of the mission, "he met with Bin Laden to discuss the targets: the World Trade Center, which represented the U.S. economy; the Pentagon, a symbol of the U.S. military; and the U.S. Capitol, the perceived source of U.S. policy in support of Israel.
According to testimony by Philip Zelikow, bin Laden was motivated by a desire to punish the US for supporting Israel and wanted to move up the attack date.