After my initial shock at hearing the verdict and my attempt to rationalize it I have further reflected on the verdict.
Perhaps it all comes down to the difference between Canadian and Floridian/American attitudes to vigilantism.
I consider myself to be a reasonable man and my interpretation of self defence does not allow for an aggressor to claim self defence. For example, you cannot start a fight with someone and kill them and then argue that because they fought back you killed them in self defence.
In this case, perhaps because the actual physical altercation was not witnessed, the jury seemed to have difficulty seeing who the aggressor really was. I had no difficulty determining that at all. The aggression started with the vigilante stalking of Trayvon Martin (who was doing nothing wrong) by George Zimmerman. George Zimmerman was clearly the aggressor. George Zimmerman killed Trayvon Martin. George Zimmerman was guilty of murder.