Even if he hadn't needed to fight Zimmerman, it really doesn't sound like Zimmerman had any need to kill him. Then you throw in the fact that Martin did need to defend himself, and it's just a big mess of Zimmerman-was-super-wrong.
As for "he didn't have to fight Zimmerman." So what are you supposed to do when you are being stalked by a stranger who is potentially armed? This is a serious question; I keep hearing what Trayvon did wrong, but I never hear what he should have done. If he tried to run, he "looked suspicious," because "why would he run if he wasn't guilty?" If he stayed to fight, "well he started it." It seems like people will judge him harshly no matter what he does, while simultaneously absolving Zim of any (moral) guilt no matter what he could or should have done differently.