Foxnews just said that one of the hijackers didn't even have to force his way in the cockpit door. They let him in willingly, as a courtesy, when he showed his fake pilot license and he was allowed to sit in the jump seat in the cockpit right from takeoff. They got this info from the flight recorder, and I missed which one. The only flight voice recorder I thought they recovered was the one at the PA crash site. Not sure though.
Wow, that is really screwed up! I wonder if the other hijackers gained entry in a similar fashion?