The Detective 2 (2011)

Bumbling private detective Chan Tam (Aaron Kwok) is enlisted by police pal Fung Chak (Liu Kai Chi) to help in the investigation of a serial murder case. The victims--a middle-aged man killed at home, a dead woman found in the trash dump, and a teenage girl slain in the park--were all killed in grisly manners, but they didn't seem related to one another. With no clue to follow up on, Tam is decidedly at his wits' end. But when Chak is seriously wounded by a mysterious assailant, Tam deduces that the only way to uncover the truth is to get into the mind of the deranged killer, and in so doing he is forced to face a long-hidden side of himself.