(I realise your question is probably rhetorical but..)
have a look herehttp://www.sierratimes.com/03/07/07/article_tro_flight77.htm
most of the people "on the pentagon flight" (ie found dead at the pentagon, whether on the plane or planted after the missile hit I dont know) appear to be probable witnesses/people involved in some way with 9/11. Most where probably NOT aware of their involvement, but would have figured it out after the fact and asked too many questions. EG: (at raytheon drone facility)
2000 - bossman - hey bob, can you program a simulation airplane to hit the pentagon in this simulator we have here? we are running a millitary exercise. Bob- no worries
finished soon after
9/10/01 - bossman - hey bob, theres a conference on tommorow, here I booked you a seat on this flight [whistle] , head down tomorow ok? bob- "sure"
9/11/01 bob- WHy does this flight path look so familiar? aaaaaahhhhh