“Zimmerman had no right to be chasing Treyvon down - that is not in the neighborhood watch handbook.”
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George did not exactly “chase down” Martin. He backed off when instructed by the 911 operator.
Zimmerman left his truck in response to Martin running. He wanted to maintain visual contact. Zimmerman then tells the dispatcher he lost Martin. Both are confirmed by the phone call transcript.
Zimmerman did not “chase Martin down”. He lost sight of him.