Zimmerman was following Martin because he was acting su ious. If you take the time to watch Zimmerman's reenactment video, GZ says he would observe TM standing on the grass near a residence as if casing the place. GZ wanted to be able to give TM's location to the police which is exactly what the police want you to do.
GZ states that in the course of trying to locate him, TM walked up to him and sucker punched him. It escalated to the point where GZ had no choice but to shoot him in order to save his life. Before you call GZ a liar, watch the video. Point out specifically where you thing GZ is lying.
http://www.hlntv.com/video/2013/06/1...ayvon-shooting