The twin tower strike videos are already bad enough. Why would the perpetrators want to create more evidence against themselves? Do I really have to explain this?
There is a large amount of photos and those security video frames that any composited Pentagon video would have to agree with. It would have to be made from some previously unseen video, obviously. Surely such videos exist, but then, what else do those videos show?
How difficult would the compositing be? Are there trees in the way? Does it show the light poles? Does the explosion look anything like the shape of a plane? (I doubt it). What about the shadows? There are no shadows to deal with in any of the live Twin Tower shots, the later ones only have shadows on the building itself, an easy surface to plot shadows on (yet they still screwed it up). Plotting shadows across uneven ground, bushes, etc. is extremely difficult.
Anything which had a clear Boeing in it would disagree with the security footage frames, as whatever is in those frames is too small.
As I've said, I don't think the plane videos are CGI, I think they are videos of a real plane. These would have been shot and prepped ahead of time. They could only attempt the composite videos they planned for. Actually creating them from scratch after the fact is not a good idea.