The Fayetteville Observer is reporting that Robert Stewart's defense team may put on an automaton defense.
Basically, scientific literature shows that people on Ambien often sleep walk and sleep live -- (driving, having conversations, etc.). There is some suggestion that Mr. Stewart may have committed the shooting while in an sleep-walking state, induced by Ambien.
If this is true, it is a complete defense to the crimes. To be guilty of murder, you must have the requisite "Mens Rea"-- i.e. mental state and the requisite "Actus Reus"-- i.e. committing the underlying acts.
Mens Rea Defenses-- notably insanity -- argue that, due to the defendant's craziness, they couldn't form the necessary intent.
Automotonism, however, negates the act requirement-- if you do something when you are sleep walking, you don't actually do it. It is not a conscious act.
It will be interesting to see where this one goes (or if the Defense even offers this theory). Read the Observer article on this here.