The rest of the conspiracy theories we'll cover specifically have to do with MIHOP theories -- that the government actively designed and orchestrated the Sept. 11th attacks. Many conspiracy theorists believe that the information doesn't add up concerning the attack on the Pentagon. Unfortunately, unlike with the World Trade Center, there is no clear video of the plane hitting the Pentagon. Something hit the Pentagon, all right. But these conspiracy theorists don't believe it was a plane. Rather, they say it was some sort of military missile.
Theorists have examined the early photographs of the crash site and believe that the hole made in the building -- which was originally about 75 feet (22.9 meters) wide before more of the building collapsed -- was too small to have been caused by a 757 commercial airplane with a wingspan of over 124 feet (37.8 meters). But experts believe that not only did a wing of plane probably hit the ground before impact with the building, but that the wings would not have been strong enough to neatly penetrate the building [source: Popular Mechanics]. Some find it suspicious that windows above the impact remained intact before the rest of the structure collapsed, but these windows were blast-resistant.
Also, hundreds of witnesses say they saw the plane hit the building. And, if Flight 77 didn't hit the Pentagon, where did it go? More importantly, what happened to the victims who were on it? Perhaps, say theorists, they were put on Flight 93.