I feel you...but let's face it: both of them are going to get caught sooner or later and we all know that no matter if sangwoo lies, in the end he's going to get arrested as well once they destroy all his alibis for the rest of the murders. I mean there's that policeman who already suspected of him...the only bad thing is that even if Yoonbum isn't caught he's going to stand for Sangwoo, because he's being brainwashed. *cries*
if the police does good job (which i doubt, because that one policeman is the only one competent there, apparently) bum would be sent so psychiactric clinic and not to jail.
If them reporting a Missing Person case works out and leads to Sangwoo being a killer, then, damn I'm thankful that they reported it. Though I have a feeling that if it was ever found out that Jieun went to Sangwoo's place, Yoonbum will also get tied into the whole murder (because let's face it, he was a part of her death) and worse case scenario: everyone in Jieun's group of friends will put the blame on him because they were never really fond of him and would most likely fall for Sangwoo's lies (if he tries to lie that he has nothing to do with her murder).
I feel bad for Yoonbum, though. The way he got tricked by Sangwoo and then was being brainwashed that all those murders that Sangwoo commited were all his fault; this poor babe is going to go through so much hell for when he is saved and has to go through therapy :( Like, he was even crying because he was scared about going outside. Jesus, someone needs to save him - fast!