Then why did he bother to ask " what are you doing here?" If his goal was to kill this kid all along, why bother talking to him at all? And why were they wrestling around on the ground? Why would GZ knock TM onto the ground if he was planning to shoot and kill him?
Excellent questions. The answer is that I don't know.
The following is my opinion:
I believe that GZ intended to kill TM while talking to 911. That was the script he was working off. : crazy black guy, on drugs, looking this way, checking him out, coming toward him, hand in waistband, holding something, please send an officer...
Dammit he ran!
Note that none of these assertions were expanded upon, as one might expect in normal conversation. They were simply thrown out there, one after another, like breadcrumbs on the self-defense trail. Three problems: first people don't talk that way; second: IF an unknown drugged up stranger was approaching your vehicle looking like he had just pulled a weapon you wouldn't open the door and hop out, you would hit the gas; third: none of this nonsense fits Trayvon at all, he wasn't a gang member, he didn't have a gun, and he damn sure wasn't interested in a confrontation with the strange dude. In fact, when the strange dude opened his car door and started to get out, something in his body language scared Trayvon so much he run away.
Once Trayvon ran GZ was off the script and winging it. Now he's ANGRY. It's not going the way he intended. He had this nice self-defense script all worked out and the kid screwed it up.
What actually happened during the final confrontation we will likely never know. We do know that there wasn't some epic beatdown, and we know they weren't even particularly wrestling on the ground. We know this because you can't really wrestle and scream like that. It seems a safe assumption that Trayvon's final minute was spent begging for his life.
But that's all just MY OPINION.