a relationship with a boy known as Jong-pal, who had escaped a sanatorium. Do-joon attacks another prisoner who calls him "retard". On one of his mother's prison visits, Do-joon recalls a memory of her attempt to kill him and then herself when he was five by lacing their drinks with a pesticide. She tries to apologize, saying she wanted to free them both from hardship, but he tells her he never wants to see her again. The mother learns from a camera-shop worker that Ah-jung had frequent nosebleeds and had pictures on her cellphone that she wanted to have printed. Ah-jung's friend is attacked by two young men who are looking for the phone, but the mother rescues her and then pays Jin-tae to interrogate the men, who claim that Ah-jung accepted rice in exchange for sex (and was nicknamed "the rice cake girl"). They say she used her phone to secretly take pictures of her partners, thus making it a potential tool for blackmailing. The mother tracks down the phone, which is hidden at Ah-jung's grandmother's house. Do-joon remembers seeing an elderly man in the abandoned building on the night of Ah-jung's death and identifies him in one of the pictures on Ah-jung's phone. The mother recognizes the man as a junk collector she once bought an umbrella from and goes to his home to find out what he saw, on the pretense of offering him charity medical services. The collector reveals that he has been troubled since he saw Do-joon kill Ah-jung. He witnessed the two have a short conversation, during which Ah-jung called Do-joon a "retard", and Do-joon then threw a large rock into the shadows in which Ah-jung was standing, hitting her in the head and inadvertently killing her, and then dragged her to the rooftop. Unable to accept the truth, the mother frantically tells the collector that Do-joon is innocent, but the collector picks up the phone to finally report what he had seen to the police. Fearing for her son, the mother bludgeons the collector with a wrench and sets fire to his house. Later, the police tell the mother that they have found the "real" killer: Jong-pal, who is being presumed guilty after Ah-jung's blood was found on his shirt. The police assume it got there during the murder, but the mother realizes that Jong-pal's story, that the blood is the result of