I can't make anything out of this movie. Serial killers is just low-life butchers. He just wants to kill women. And police with proper high-tech Korean technology can catch a killer because our lousy serial killer threw 12 tons of evidence at the crime scene. It's like he doesn't care about anything because he himself called the police after committing murder.
In the meaty part of the movie, both the killer and the brother had infinite chances to kill each other or the deaf girl. But they just threaten each other with knives. It's a mess. They're just trying to make the audience emotional by portraying meaningless scenes, which can't be performed when a serial killer is after you. Normal people seem to not understand anything; they just take anything at face value.