[Yardstick]

Good points. It does seem very plausible that Zimmerman was pursuing Treyvon only in the sense of keeping him in sight for the police.

[Verginius Rufus]

Excellent summary. The only reason the confrontation happened was that Trayvon noticed Zimmerman watching him and chose to confront him. Was it just because he felt disrespected that he was being observed, or was some drug in his system causing him to behave violently and irrationally?

From the video taken at the store, we know that Trayvon had much more time than he needed just to return to his father's place. He may have been wandering around looking at the unlit townhomes for some time before Zimmerman spotted him.