The Trayvon Martin shooting is a case that you just can not simplify in to talking points. I am researching this and am finding it hard to get factual information as opposed to commentary but the more I find out, the more my opinion has shifted. MSNBC (especially Al Sharpton) has already convicted Zimmerman and Fox has already exonerated him and they are doing it by selective reporting of facts. To their credit, some commentators on both channels have condemned the trial by media.

Regardless of how it is reported on any given outlet, there are some indisputable (or at least nearly indisputable) facts to be considered.
As a Concealed Carry Permit holder, Zimmerman had an ethical (but not legal) duty to avoid putting himself in a situation where he may need to use his weapon. He pursued Martin, even after being told by the 911 operator "We don't need you to do that". Zimmerman's actions were absolutely stupid and reckless. HOWEVER, when adding up all of the witness accounts, 911 calls, autopsy results and physical evidence so far, I have come to a few logical conclusions. Most importantly, that Trayvon Martin physically attacked Zimmerman and he did not do it because he was scared. He did it because he was mad and considers himself a badass. It makes no logical sense that Zimmerman started the fight because no one in their right mind that carries a gun would instigate a physical fight with another person and risk loss of weapon retention.
Zimmerman clearly did not track Martin down to shoot him in cold blood because he was the one who called the police. A shallow case could be made that he was trying to fake an alibi with the call but I'm going with Occam's Razor here. Martin had a phone but did not attempt to call for help. He was on the phone with his girlfriend. She says he stated to her that he was being followed and was scared, however there is no confirmation of that and it seems to go against what is known of Trayvon's personality prior to the shooting.
Zimmerman had not presented his weapon before the attack. Regardless of what anyone thinks of smoking pot, it is illegal in Florida and the autopsy showed that Martin had smoked it recently but I don't think anyone, high or not, is crazy enough to start a physical attack on a person that has a gun pointed at them. There is no question that the scuffle began a good 30 seconds before the gun was fired.
Martin had only two injuries, the fatal gunshot wound and an abrasion on his finger consistent with a closed-fist punch. Most eyewitnesses put Martin on top of, and beating Zimmerman, not the other way around. Zimmerman had a broken nose, facial fracture, cuts to the back of his head and his shirt was grass-stained on the back.
No one can really tell who's voice is screaming or if it is indeed calling for help. The screaming stops at the point of the gunshot so it is consistent with either Martin stopping the screaming because he was mortally wounded or Zimmerman stopping the screaming because he no longer feared Martin. It makes more sense to me that it is Zimmerman yelling because he is being beaten and is sure that if Martin gets his firearm then he's toast. If it is Martin screaming I suppose it's possible that he realized Zimmerman was armed and then feared for his life, knowing then that if Zimmerman got control of that firearm then he would likely be shot - which is exactly what happened.
From a legal standpoint, I believe the prosecution has overcharged Zimmerman. He had a permit to carry the gun. While inadvisable, it is not illegal to follow someone that you believe to be engaged in nefarious activity even if that suspicion is erroneous and born of some level of racism. It is not illegal to ask a stranger what they are doing. The first illegal action in this event was Trayvon Martin physically attacking Zimmerman. IF at that point, Zimmerman feared for his life, he was entirely within his right to defend himself with his firearm.
Both of these men could have prevented this tragedy. While he had no legal obligation to do so, Zimmerman could and should have stayed in his car and waited for the police. And while Martin was doing nothing illegal at that time, and had a perfect right to be where he was, he could have simply told Zimmerman where he lived and that he was just walking home OR simply ignored him and continued home. I believe that if he had done so, Zimmerman would not have drawn nor fired his weapon and Martin would be alive today.
I think a more appropriate charge would have been 3rd degree voluntary manslaughter or maybe even involuntary manslaughter. I'm not sure if the jury can reduce charges but if they can't, I do not believe they will convict Zimmerman on 2nd degree murder. I could be wrong, I famously and embarrassingly blew it when I predicted the 1st degree murder conviction of OJ Simpson on the silly assumption that the jury was intelligent and impartial. I also lost 5 bucks on that one so I'm not betting this time.
In any case, it is fruitless to try and define this as a black and white case. It is very, very gray.