“I am speculating as well, but the evidence is what it is and was clearly an act of self-defense on Z’s part.”
How can there be any speculation? The wounds on TM are the gunshot wound. The wounds on GZ are a smashed nose and cuts & scraps on his head. Could GZ’s wounds have happened after TM suffered his gun shot wound? Extremely unlikely. If TM had other than the gunshot wound (or scraped knuckles) then there would be room for speculation, but there are no such wounds. TM assaulted GZ. The physical evidence, the eye witness, all support this conclusion. There is no evidence otherwise.
The take away (the moral of the story) is NEVER assault someone. There is NO telling how it will end.
You cause me to change my tag line.