They knew the attacks were going to happen and so did Stevens. It could have been prevented! Stevens warned them well in advance.
Am still thinking the moles or a mole at State decided he had to die. Not certain why that was thought, but the Ambassador is gone. Maybe is as simple as the plan concocted was not the way it went down, in more ways than one. D.C. is full of murderers, and most of them wear suits, or dresses (barney the frank alternates) and carry briefcases and oh the power of the purse.