We are all sinners & all deserve death. The wages of sin is death.
IMHO:
Most likely TM was pounding Zim's head into the concrete when TM got shot.
One lesson one should get from the Zimmerman thing is that if one is going to carry a gun, one simply has to also carry something like a Kimber Pepper Blaster, which is a little plastic red pepper gun, quite powerful. I say that because if one is carrying a gun and gets into a fight, it will likely become necessary to use the gun before the attacker grabs it and uses it on the one resisting.
The Pepper blaster is needed to defend the gun. You do not want to gun-shoot someone who is only armed with fists and concrete pavement. Even though it looks like Zim was justified, his life is ruined, he did jail time, and ended up with a huge debt over a million dollars. So much for our injustice system.
But if Zim had been walking around looking for a suspicious person (bad idea anyway), if Zim had been carrying a Pepper Blaster in his hand, probably nothing would have resulted if he was ambushed by TM, like jumping out and confronting him. If TM had seen that blaster in Zim's hand, likely nothing would have happened, or at worst Zim would have pepper-blasted TM.