I am not smart but I think that after the mom felt like her son is growing up to be more like his father, she started to get more insecure and probably beat sang woo, and then her insecureties turned to madness and ended up killing the father. Which explains why he kept testing bum to make sure that he will not kill him like his mother did.
Did anyone notice that he was watching inside out?
No, until you mention it XD