Responses
The police officier asked all Gusam's friends to comes for interrogation.
This kid was not his friends but hangs out with them. Seems like he's mistreated by K and wants to take this chance and report it to the cop but didn't since K threatened him. The cop seems to have understood there's something fishy with the kid but didn't dig further. At least, that's what I understood.
Chapter 16 shows K's relationship with that kid, he's the one in his underwear. Chapter 30 shows what K did the night before Gusam woke up to the bloodbath.
I had a hard time following what happened with the police officer and that kid this chapter. Could someone explain?