I'm sure they'll arrest him when they have a solid case. It seems pretty clear that both parties were scared of the situation that Zimmerman's paranoia created. If a struggle ensued and Martin got the upper hand and was then using unnecessary force to fend off his assailant... then what?
Yes it's terrible that a paranoid coward was able to kill an innocent kid over a misunderstanding created by his own paranoia but if Martin became an actual threat to Zimmerman's life at some point then there might not be enough of a case.
Zimmerman is a nut but I doubt he was looking for a way to kill a young black kid without reprisal from the law. He was being a paranoid idiot, and probably due to race confronted a kid he hadn't seen before, shit got really fucked up, and now Trayvon Martin is dead.
No, there would still most definitely be a case