Sangwoo got the knife to kill the police officer in the event that he found Bum. He probably took the knife when the police officer turned to check upstairs. He hid the knife in the back of his pants. Sangwoo gets ready to kill the police officer here http://www.mangago.me/read-manga/killing_stalking/mf/c013/32/
But I think bum is gonna stab sangwoo,
Hm...? What makes you think like that?
The knife off the kitchen counter was in the back of Sangwoo pants. He slipped it into his pants and covered it with his shirt. It shows it in a panel of the manga.
Yeah I know, that's what my comment said. .__.
Sorry, I realized after I put mine on there that you had explained it as well.... LOL
Idk I just feel like it
Hmmm I wonder where the knife is....and I wonder If the black hair guy gonna stab that guy, god dammit I forgot there names