SoliderDad read all the posts - I have learned more about this incident on this thread than I had on others.
The State is investigating
The police did investigate all the evidence - unless Zimmerman changes his statement there is nothing left to consider. Read his father’s statement as well.
That boy made a poor choice to attack an armed man - sadly he is dead. But its time to move on.
I’ve read enough to know that there is nowhere near enough facts to make a determination of who was responsible. And, there is sufficient reason to have an independent investigation. There are investigative techniques that can be utilized to look for a better understanding of what took place. Not investigating because the shooter has claimed self-defense is a horrible reason to drop this matter.