The injustice is not that his killer is not black. Nor does justice lie in that George Zimmerman is not white. You don’t have to be white to act from a place of irrationality and strange fears. Justice and injustice lie in the aftermath.
This is why I ask friends and members of my own brown family who tend to indulge in throwaway racist remarks about black people and the president not to do so. First, you are the cause of “the decline of civilized society” about which you complain so loudly, but, more importantly, such talk only makes it easier for Americans to look away from Just Another Black Kid Getting Killed. That’s injustice. Don’t do it. Don’t have any part of that mind rot.
As for justice, here’s an exercise: Compare the reaction of the Sanford police to a) the circumstances as they are and b) if Martin had shot Zimmerman in self-defense, because he felt threatened by a crazy, older dude following him on a poorly-lit street. If you came up with very similar answers, I’d like to move to your world.