I.Saw.the.Devil.2010.KOREAN.1080p.BluRay.x265-VXT

The police have been hunting psychopathic serial killer Kyung Chul (Choi Min Sik) for a long time, but he slips away each time, leaving behind him a gruesome trail of blood. He has taken the lives of many in the cruelest possible ways, and his latest victim is the fiancee of government agent Soo Hyun (Lee Byung Hun). Soo Hyun vows to avenge her death at all costs, but to catch the devil, he too must become a devil.

https://www.imdb.com/title/tt1588170/reference/