It was an Asian movie I saw a few years ago. Had martial arts and drama. I remember that the detective had to cut off his own arm near the end of the movie in order to save what I believe was his son from his father who was a martial arts master but also corrupt and evil. The detective was trying to solve a murder that happened in what I think was a paper mill and the movie kept changing perspectives of possible motives and characters. Any help would be greatly appreciated, thank you!