I'm thinking Sungbae only said that to get Bum to tell the truth. I'm confused how he found out Bum killed Min Jeun or whatever her name is. That could've been a set up too, but I don't know about that.
Remember when his friend was on the phone with him saying the cops think bum is a suspect because of how badly she was talking about him.
I was so frustrated when bum wasn't telling the truth, and how is sangwoo free after he confessed to everything???