Sympathies aside, the facts as I recall them (we've discussed this one before) were homicide.
http://forums.pelicanparts.com/off-topic-discussions/477561-gun-self-defense-guys-what-your-take-pharmcists-actions-video.html
No reasonable basis to think the victim was a threat (prone, wounded, no weapon, defendant walks by the victim/turns his back on the victim as if he knows the man has been neutralized).
Actions consistent with deliberation (walked outside, came back in, walked to counter, retrieved another gun, walked back to victim, aimed, fired 5X).
Presumably the evidence at trial showed this.
My guess - the defense would have needed to show something involuntary like a mental blackout (layman's term), but didn't. IIRC, the defendant went on a TV show to talk about it - he or his lawyer or both are fools - that probably foreclosed a lot of potential defense arguments.