If the prosecutor can "prove" that you didn't fire intentionally then he's also, by default, proved that you didn't fire in self-defense since self-defense is an intentional act, not an unintentional one.
But then it's an "accidental" shooting and, at the very least, knocks down the charge from murder to negligent/reckless homicide. I've never heard of a prosecutor charging on such a theory and the defense claiming I shot him/her intentionally but to defend myself. In my neck of the woods, that would earn the defendant an amended charge at trial and a murder instruction.
So, I really don't think this is very realistic but I cannot categorically say it's impossible.