I'm not so interested in their past (but I still like the incest tho). From the very first chapter until now, I always think about the police who introgated Yoseob. I mean, Yoseob keep silent all the times, and he suddenly speak the truth (or the past) after "that person" came to view.
I guess Yoseob killed 8 people when he's 3rd year, and Jaeha already graduated. And the person who introgated Yoseob in prolog was Jaeha. Just guessing.
I think it was because the police guy ressembled Jaeha physically (at least, from what we can see, he has the same hairstyle and hair color).
BJ Alex? Sounds like BIJI ALEX
BIJI = that 2 balls under penis
Or blowjob Alex ( ̄∇ ̄")
Kok ngakak X'D