Unlike in movies, in real life when someone has decided that they are going to shoot or kill somebody experiences a massive rush of adrenaline as they are winding up to actually do the deed.
Granted, there are probably Mexican drug cartel killers who don't get worked when they are about the shoot someone, but that's not how normal react to life and death.
Here is a recording of a man who observes burglars at his neighbor's house. He states early on, and throughout the call that he is willing to shoot them. As he sees them exiting the house, he decides that he needs to go and stop them. You can hear the tone of his voice change, the pitch gets higher, you can hear the stress as that adrenaline rushes in and he prepares himself for violence.
Man shoots burglars.
Let's now listen to George Zimmerman's call to the police. His tone stays pretty calm and even the whole time, which is consistent with someone who is not ramping themselves up to go shoot somebody.
(There is some swearing.)
Either George Zimmerman is Han Solo, http://youtu.be/mu-TZpGdszA?t=1m47s or a cold blooded mass murder, or he wasn't planning on shooting Trayvon Martin.
Just my two cents.
3 minutes ago