Lawless (2004)

DI John Paxton begins to question his job when a murderer walks free from court because of a legal technicality. His boss DCI Pete Chambers is equally disgusted by the outcome and plots the ultimate revenge - killing the culprit himself. Paxton refuses to get involved, but later discovers Chambers dead in his car - and ends up being the chief suspect for the crime and goes on the run - all the while trying to prove his innocence by finding the real culprit.