I would tend to agree, pawnmower, and I think you and I were typing similar thoughts at the same time.
My thinking is that the family is going to want to see this guy hung from the nearest tree, and I can't blame them at all. Being hanged from the nearest tree is not unreasonable. However, I don't think it's Murder 1. The guy thought he was doing something good, but because he was stupid he murdered an innocent person. There is no right answer beyond, "he needs to be punished for this".
How do you think the prosecution's case goes down the tubes if Zimmerman was yelling for help? If I'm the prosecution, I say, "Dude attacked a kid and the kid was defending himself. If Zimmerman is a wimp and started crying, that's his problem. It's not allowable to murder a kid who fights back when he's being attacked."
My ancestors fought cave bears so I could make this post.