(V): And the video did show a man with his hands in his pockets being hit and pushed from behind.... since when has that been legal?

Its legal if during a riot, the police command you to show your hands, and to move out of the way.... as far as i know, it is ilegal to disobay any command from a police officer, and they always have a right to force you to comply.

Now if, during this procedure, you have a heart attack, or you bang your head and end up dead, then that is not murder, and it is your own fault you are dead, or it is a coincidence, and you would have died of a heart attack anyway.

I am NOT saying this is what happened, but it is possible that a video doesnt tell the whole story, and like Snoopy said, if it was all as clear, cut and dry, as it appears n the video, then this investigation would have ended long ago, so the length of time it is taking tells me that your first assumption, that it was clearly murder, is WRONG