Not guilty, sure. Not responsible for his current misery? Hell no.
I remember being stalked (and eventually mugged). I felt someone was behind me, but it was too dark to see. I had no safe avenue to safety. I got closer to my destination and I felt the hand on my soldier. The reality was that I was so freaked by the prior few minutes that if the person that approached me only wanted directions...I believe my response would have been the same. I went nuts on the guy and I got lucky. When he was down on the ground I kicked the **** out of him.
You do not stalk people. Especially in the dark.
But yeah. Zimmerman was not guilty, but personally responsible for his current situation.