Korean movie

Yoon Do-joon is a boy with a mental deficit who lives with his mother in a small town in South Korea. One day, a student's body is found on a terrace in a strange position, throwing the whole country in despair. The little and no overwhelming evidence prompts the boy, so much to police enough to accuse him of murder and immediately close the case. But her mother is convinced of her son's innocence and will do anything to find out the real culprit.