Well, as I said, I am not sure I am capable of seeing what you mean. I am not sure I understand what the legal question of murder is so I can't really know if I'm concerned or not. I am sure you mean something quite relevant by the 'legal question of murder' but I don't know what.
All I know is that a man with a gun went after a teen with candy walking home from a store and the kid wound up dead. I know that the man was told not to go after the kid and did anyway. I also know that by Florida law the kid had a right to kill the man because a man with a gun coming after you is a deadly threat. So the Florida law designed to protect the kid got turned on it's head. Of course, had he beaten the man to death before he got shot, he would likely have been arrested and charged with murder.
Negative on Martin being allowed to kill: If you believe Zimmerman's account, he was returning to his vehicle when Martin approached him. If this is true, both Martin AND Zimmerman are complete idiots. If Zimmerman just was following Martin and then Martin turned to confront Zimmerman and then Martin attacked Zimmerman, Martin is still in the wrong.
You must fear for your life (or in my state, the lives of others) before lethal force is allowed. If someone just walks up to me, gets in my face and yells at me...or is just following me around, I cannot turn around and shoot him. If when I turn around he brandishes a gun while moving towards me, or pointing it at me...or even a knife...then I fear for my life, can stand my ground and blow a hole through him.
My point is that we have ONE witness account of the attack itself, the rest are people in their homes who did not see clearly, or people commenting on what they say AFTER shots were fired. That singular witness account says Martin was on top of Zimmerman immediately before the shot was fired. That's not to say this clears him, for all we know he started a fight and ended up losing badly, so he pulled his gun. But evidence does seem to support that at some point, Martin was on top of Zimmerman hitting him.
The burden for the law is to prove that Zimmerman killed while not fearing for his life, or that he started the fight himself (following != starting) - if they cannot prove that, Zimmerman walks. And if Zimmerman walks, I fully expect to see a repeat of the Rodney King riots.