I have never understood why Hana's mother was killed. She was propped up as if on a stage to be judged for what? For being homeless? For being a homeless minor taken in by an abusive adult man? For hiding her kid out in the center instead of keeping her at the killer's home?

I might very well have missed some context as I always do something else while watching tv shows, but I just cannot for the life of me understand why she was killed,

in his eyes the child was in danger with her (eun ho specifically had only one conviction i.e., to save the child at any cost while his brother had a much stronger conviction of judging them). which is kind of true since the younger one died in front of her and she didn't do shit. although this was discovered later.