This is part of the problem with this discussion. I think the cop should be prosecuted/disciplined/etc... But just because the cop screwed up doesn't mean he wasn't just trying to do his job. Once the situation became physical all bets were off. Cop wasn't intending to kill him, he was intending to subdue him most likely using a technique he has used many times. This doesn't excuse the action, but it also doesn't mean he had murderous intent. Poor training + poor police philosophy = a bad unintended result. Turns out this bad results was the worst result possible, and a man who had committed a petty crime lost his life.
Labeling the cop as an intentional murderer does nothing to advance discussion, and is a huge part of the problem. Both sides of this issue are quick to label (criminal/murderer/racist/thug), and that is completely unproductive and narrowminded. In Garner's case he deserves punishment (I am in no place to pass that judgment, but just my opinion). More importantly the system of over militarization of our police needs to be put under great scrutiny. Instead we have people calling individual cops murderers and racists, which will do nothing to prevent this type of action from occurring in the future.