This murderous South Korean tale comes from the accomplished Kim Ji-Woon (A Tale of Two Sisters).
I Saw The Devil (in Korean with English subtitles) stars Choi Min-sik (of the grotesque, yet very powerful "Oldboy") as serial killer Kyung-chul who offs Ju-Yeon, the pregnant fiancee of a government agent (Lee Byung-hun) who has been tracking him.
Once the agent gets to him and leaves him alive enough to escape with a homing device, more horrific crimes will be committed. Apparently, so that Kyung-chul can experience what the victims did (before their demise).
I Saw The Devil obviously is not for the faint of heart and has the length of some epic-minded features. As much as this is consistent guttural horror, a dextrous Ji-Woon and his capable actors make it diabolically twisted cat-and-mouse pulp augmented by a moody soundtrack. In a strangely masterly, one is held prisoner by a well-executed shocker of bloody revenge.