Call me crazy, but what if there are others?
What if the FBI, Military Intelligence, or Homeland Security know of others - in the military, or driving a cab in Manhattan - and haven't told one another or us. Or what if some U.S. intelligence agency gave them a free pass so as not to be perceived as politically incorrect or racist - you know, so as not to discriminate against Muslims? After all, the U.S. knew of Hasan's ties to a radical cleric.
There have to be others out there, doncha think?