if you look at this, it seems more likely that zimm was lying in wait to ambush martin. zimm was tired of those assholes always getting away and looking like a fool every time he called the cops (and there were a lot of times).
zimm lies in wait, martin thinks zimm is gone and lets his guard down. zimm pops out and confronts him, the chase that witnesses describe starts at about the T where zimm's key are dropped (maybe because he was drawing his gun). zimm tackles martin as martin runs for home, martin's phone goes flying. martin pops zimm in the face, zimm's super anger mode is activated, and out of anger or confusion, zimm shoots martin.
of course, that is all just conjecture, but how else would you describe the locations of the objects and the murder?