My opinion of this entire tragedy is that both TM and GZ poorly handled the encounter prior to the actual shooting. I've tried to put myself in the shoes of both of these men and I've thought about how I, myself, would've handled the situation. Maybe I'm naive, but I would hope that most people, if they found themselves in a similar situation, would choose to act in a manner that is at least in line with what I'm outlining below. Of course, all of my suggestions could be moot anyway because of the highly charged atmosphere of the confrontation along with the darkness and the uncertainty (and many other factors) which would quickly degenerate into a scenario where anything can go.
Firstly, if I were in GZ's shoes, I would've clearly identified myself as a neighborhood watch member to a clearly agitated TM in order to calm him down by reassuring him that I did not have any random aggressive intentions. I would have clearly stated that my only intentions were to ascertain TM's intentions in order to safeguard the neighborhood and I would've also explained that I had called the police already. At best, TM would've realized that nothing bad was going to happen and things would have been cleared up in quick order. At worse, TM would've hightailed it out of there knowing that the police were on the way.
Now, if I were in TM's shoes, I would've refrained from using such a confrontational manner toward GZ and not so quickly assumed that GZ had harmful intentions as soon as they had met. Perhaps he could have allowed more time for GZ to explain why he was following TM, and he would've realized that there was no need to defend himself.
Again, this is just my opinion, but it seems to me that both of these men are guilty somewhat of puffing out their chests and playing the tough guy. GZ is the tough guy cop wannabe with an authority complex while TM is the street wise gangsta wannabe. Pitting these two volatile personalities against each other was never going to end well. Both of their attitudes contributed to the quick escalation of the situation when cooler heads could have prevailed instead. We could go over endless what-if scenarios where either GZ or TM (or both) could have approached things differently and more rationally, thereby avoiding tragedy altogether. Unfortunately, cooler heads did not prevail and a young man is dead.