Murderer (2014)

Joo Hyup is a cold blooded serial killer, but he tries to live unnoticed in a small village with his son Yong Ho. His son becomes friends with Ji Soo, who is a new transfer student at his school. Ji Soo soon realizes that Joo Hyup is a serial killer. Joo Hyup decides to kill Ji Soo for himself and his son.

I guess I could say... Both of these movies try to ask the "Are monster born or made?" question.