Why do cops get away with murder?

last night there was a small riot in oakland for the brother that got shot in the back at the bart station..he had no weapons + he was handcuffed & the racist cop still shot him in the back..this happened on new years day when this brother was shot..this cop should go to jail & they should put him in with the general population so he can get beat down..here is some footage from last nights riot http://www.youtube.com/watch?v=HeDjJf02fac