I've just been for a run ( ) and had a think about this. I think the basic point is this. Ignore the fact that he shot the guy in the back. Just answer this question:
For leaving the burglar bleeding to death on his property, checking into a hotel and not alerting the emergency services, is TM guilty of a crime?
I dont think that there is any reasonable argument to say that he is not guilty of a crime for doing that. Ok. So if he is guilty of that, it's simply a matter of deciding what he is guilty of. Manslaughter seems to be the correct crime IMHO. He didn't mean to murder the guy, but his actions did kill him.
I think if you look at it in this respect there is no argument to say that he should not have been jailed. I think he received the right sentence tbh...