Responses

they didn't but i'm saying it seemed like geumsoo knew?
when namsoo transferred in, he smiled as if he knew something
when namsoo started to get bullied, geumsoo told the bullies to leave them alone for a while, to "let them become friends for now"
and in general he seemed to know about namsoo's psychotic capabilities
how did the policeman's son (the now-cripple) know namsoo was geungho's brother? because earlier, he told the bullies to leave namsoo and geungho alone for a while.
and when namsoo was confessing, toward the end he was talking about how he sent pictures to the policeman's son and then the son got ballistic and beat namsoo up, what was up with that?