If he is tried he will be tried for violating the decedent's federally-guaranteed civil rights in a federal court, which are different charges in a different jurisdiction.
One thing about the whole story that strikes me as very questionable is Ofc. Mehserle's contention that he confused his sidearm with his taser and that he intended to tase Grant, not shoot him.
This claim is simply not believable. The weapons look and feel and weigh differently from one another and in these situations muscle memory kicks in.
It seems very unlikely that he would have drawn from the opposite side and pulled out a heavier weapon with a different handfeel and not have noticed. This would be plausible if he had switched the normal positioning of the respective holsters, but he hadn't - they were where they usually were.
It was a reasonable verdict and Obama knows it....just like Obama knows he has to keep black Americans stirred up and believing they are oppressed. Otherwise where would the commies get their votes?