I believe Zimmerman pulled his weapon only after he and Martin exchanged words. But I also think Zimmerman wanted to provoke an angry response from Martin so that he--Zimmerman--could have the final word by pulling his gun. I don't think he thought it through beyond that point and didn't count on Martin attacking him or figured if Martin did attack him, he was just killing some scum-ass burglar who had it coming.

What I'm curious of is the witness's statement that she saw Zimmerman standing over Martin's body with his hands on him. What was he doing? Looking for a weapon? Was he convinced Martin was armed and that he would be exonerated for shooting him? I just wonder what was going through his mind at that moment.