Guys,
Eyewitness accounts are notoriously unreliable. That applies to all situations, from air disasters to purse snatching.
There's a famous little experiment that a lot of Psych 101 professors perform with unsuspecting classes. They prearrange for one of the students to just get up in the middle of the class go to the front of the room, do and say something and simply walk out. The class is then asked to describe the whole scene.
You'd be amazed at the descriptions of both the person and the actions that come from these surprised eyewitnesses. (I remember stating her sweater was blue - try green).
It's for this 'phenomenon' that both accident investigatos as well as defense lawyers take "eyewitness" reports with a grain of salt.
But to be fair, I was a little surprised as to how quickly the NTSB flatly stated this was not a terrorist act.