As far as the person on top, Zimmerman said that after he shot Trayvon, he got on top of Trayvon and stretched out his hands because he thought that Trayvon had something in his hand when he was hitting him. Do you think maybe this is when the people saw Zimmerman on top? At least one witness said that only one person got up-- the one on top. Then the person on top started walking back and forth. Then the neighbor came out with a flashlight. Trayvon's pants had grass stains on the knees. George's clothing had grass stains on the back.
If the jury goes by the law, they have to assume that Trayvon started the fight because there is no evidence that suggests who started it. If there are two possible outcomes, one that suggests guilt and the other that suggests innocence, the jury has to go with the one that suggests innocence.