Even if he wasnt assulted, as long as he didnt shot him in the back, whos to say he wasnt scared for his life anyway. He could just say he thought Martin was going for a weapon and so he fired. This law is so dangerous and it protects criminals.
And the facts are that Zimmerman, a grown man, was stalking random people at night with a gun. Just this fact alone should tell you that this guy is dangerous.