Dan White shot the mayor and a supervisor in cold blood and confessed everything to the cops. They managed to stop him from spilling out his premeditation on tape by interrupting him as his confession was getting rolling and the DA failed to win the easiest conviction of his career. The cops then went on a spree of beating people gratuitously in the Castro.

Cops aren't there to enforce the law without fear or favor. They routinely engage in petty corruption and complain when they have to be professional when on duty.