those who investigate all this know it was a missile and if you look well here you  can easily deduce the same thing;

A little seen early photo of the Pentagon after it was attacked on 9/11: Was this damage really caused by a Boeing 757, as was officially claimed, or was it caused by something smaller, like a missile?...........https://www.reddit.com/r/conspiracy/comments/1cmdspr/a_little_seen_early_photo_of_the_pentagon_after/