context: After her young son accidentally drowns, a woman has a breakdown and is finally placed in a mental hospital. After her release, her husband takes her for a weekend at a secluded country mansion, hoping to help her recover. However, things at the mansion aren't quite what they seem to be, the couple begin to feel an uneasy and oppressive presence, and the mother starts to see things that may, or may not, be hallucinations.
question: Who killed Ga-in's parents?
answer: Hyun-joong