Wait why is the young guy a psycho? I totally forgot what happened
He wants to kill the dude who killed his father, I would too. And now he is willing to Kill for the FL sakes cause he has nothing to loose. I find those reasons very normal for someone on their right mind who had gone throught all that. I mean he is not triying to kill for pleasure, he has his reasons. He is not a psycho, just say you like the other dude more, there is nothing wrong with that, everyone has different taste.
Do you guys remember from season 1 that police who told the procecutor that if she didn´t catch Do Ki he would do it? I think JH is maybe working with that police and is looking for hints of what they do and how. He seems to kind to be the bad guy, but who knows?