Here’s all a jury needs to know: Who called 911 and who didn’t.
Zimmerman called 911. Had he intended to “hunt down” (as has been stated by some) and kill Martin, he wouldn’t have done so while on the phone to 911.
Martin didn’t call 911, nor did he ask his girlfriend to. It’s appears that he circled back and confronted Martin, believing himself to be tough enough to take him down. (That surmised from Martin’s attack on the bus driver and Zimmerman’s stating to the 911 operator that he had “lost” Martin prior to the confrontation.)
“Hey (mom, dad, friend (whoever)), I'm in the back on the walkway, which house is it. Can you meet me outside?”
If Zimmerman was up to no good he would heard, this think someone would be showing up and he would have retreated.
The most likely result would have been for him to relax and ask Martin who he was looking for.
C’mon, we teach our young kids tricks like this. If someone is tailing you in a car walk or run in the opposite direction, run places the car can't go, go to any door and ring the doorbell, start screaming, etc.