Hello Murderer(2010)

Original title: 반가운 살인자

Slacker detective Jeong-min (Kim Dong-wuk) is assigned to investigate a serial killer case. For the first time in his career he puts his heart into his work but Yeong-seok (Yoo Oh-seong), an unemployed man with natural instincts as a detective, gets in the way by trying to catch the killer as well.