Obviously Z was not to be trusted with a pistol.

But no workable law could have kept him from purchasing one. As far as I know, he had no criminal record or record of mental instability.

That's one reason the shooting is called a "tragedy." It seems not to have been predictable.

With 200 million guns in this country, it's a credit to Americans that such a relatively small proportion of the 300 million population are shot.

Unless the state can prove premeditation, Z won't be charged with first-degree murder. My guess is it would be some level of manslaughter. There's even the possibility of "negligent homicide" (the terminology varies from state to state)if, for example, Z simply drew his gun as a threat without actually pointing it at M. It may all depend on the details of the scuffle.

The point is that, even if convicted, Z is unlikely to go to prison for life without parole.   

P.S.: Just being Hispanic doesn't mean a person can't hate blacks. (Not that I've seen any proof that Z really does.)