We're still missing the most important detail here, which I think we never will hear, the actual moment of the shooting. Did Zimmerman shoot Martin during this struggle or did Zimmerman shoot him after Martin stopped and was leaving due to the anger of being beaten up (and of course there are other possibilities)? I'm leaning towards the first possibility at this point, but I'll almost guarantee that we never hear it because it would put the story to rest (goodbye ratings).
The moral of the story for me for both Zimmerman and Martin is that if you do stupid things, they are far more likely to end badly (kind of like me deciding to post over here).