President Barack Obama speaks during the 9/11 observance ceremony at the Pentagon Sept. 11, 2012. The event marked the anniversary of the terrorist hijackings of four commercial airliners on the morning of Sept. 11, 2001. The hijackers deliberately crashed two of the planes into the World Trade Center in New York and one into the Pentagon. The fourth aircraft crashed near Shanksville, Pa. Nearly 3,000 people died in the attacks.