Sin of a Family (2011)

Detective Cho is incompetent and always fails to be promoted. His only pleasures in life are spying on neighbors who are having affairs or binge drinking. One day, Cho comes across the corpse of what seems to be a child on a nearby mountain and he decides to investigate the case, thinking that this is his last chance to impress his boss. Cho enlists the help of his partner, Detective Lee, and together the two embark upon an investigation that will test their professional judgement. The more they learn about the case, the more they come to suspect that the poverty-stricken father of the dead child is their killer. But the case goes off course when the two begin to sympathize with him.