I think it is stated in the law, but it really is a matter of interpreting the law. The law specifies you can shoot to defend your self from a robbery. If he is not a threat, you are not defending yourself any longer.
Contrary to many people's opinions on this shoot, I do not have any problem defending all of the shots except the last one. And I think that one might be defensible also. He had just picked up the gun, but if the robber moved or tried to get up he is still a threat.
And there is always the old Texas defense of "he just needed killing."
I think the grand jury is a fifty-fifty chance of indicting him. Depends on whether or not the DA listens to the people and is using the grand jury to cover himself for not charging the man or not. But I give him about a 90% probability of not being convicted by a jury.