That Demon Within 2014

By a strange twist of fate, dutiful Hong Kong policeman Dave Wong (Daniel Wu) saves the life of the leader of a violent gang of armed robbers. When they commit another crime, Dave is determined to put an end to their activities. He works with the leader Hon Kong (Nick Cheung), whom the gang had betrayed, to engineer a plan to wreak havoc within the gang and let the gangsters kill one another.

But it becomes increasingly obvious to Dave and to his colleagues that Dave is suffering from a severe mental disorder, and Dave finds that instead of upholding the law as a righteous police officer, he has now become a fugitive wanted for murder.

Dave changes his plan and executes one final move that is certain to wipe out all traces of the gang and restore his reputation as a good police officer.