Latvia Calling
IMHO, answering your first point. As a pilot, the very moment I knew what the traget was, I most definitely would force the plane into the river. Therefore, I must say pont #2 is the most plausible at this time. These were kamikaze men with at least a basic knowledge of how to guide a jet aircraft. In response to 3, there must have been accomplises among ground staff at BOS, EWR and IAD in order to smuggle some type of weapon on the planes.