Every time someone fires a gun in self defense and kiils their attacker it is an intentional homicide. There is always a decision made in the instant before they fire that they are going to try and kill that person.
Ok, wait a minute... GZ obviously had no intention of killing TM because as soon as the shot fired he pushed him off and got up and asked the neighbor to help restrain him. If there was premeditation to kill, he would have shot more than once.
Plus, remember, he was surprised that TM was dead the next day.