Give us a narrative that explains the known facts better than the self-defense claim.
Aside from the fact that I've already done so, and in consideration that I can expand up my previous statements why should I when none of you have demonstrated that you are even familiar with the definitions and applicable laws surrounding the case beginning with the concepts of concealed carry (Zimmerman had a FL concealed carry permit and was presumably carrying his firearm under those laws), FL specific concealed carry laws and FL specific laws of self-defense including the castle doctrine also sometimes referred to as "stand-your-ground" although FL case law in that regard has not been particularly helpful to the cause thanks to judge Beth Bloom (chasing someone down and stabbing them in the back does not meet the criteria of self-defense under any interpretation of the definition outside of Bloom's purview).
But putting all of the above aside one of the first things I'd look at is criminal background of the parties involved. Zimmerman has a history of this kind of aggression and more importantly he stated his discontent and his intentions to the 911 dispatcher. No one can deny that he was pursuing Martin and what I've been stating from the beginning is that he had no lawful authority to do so.