Trouble debunking 9/11 plane crashing into pentagon?

I'm trying to debunk a friend who was working at the north parking lot area near the pentagon during the plane crash. Himself plus 30+ co-workers have a clear view of the pentagon and washington blvd. Yet he states no one saw a plane. I've beening looking for the past few hours trying to find a video clip/picture anything, but all I can find is crappy footage showing very little. I do believe it was a plane but so far I have nothing to back that up with. Any help would be great.