Sara was trying to hide the evidence of the murder she just committed. Hiding the body of her sister who she killed with just 5 hits on the head with a brick causing her to lose a lot of blood and being knocked out instantly, Sara panicked as she planned on killing her when she was to walk back home but since she took to long with her library studying she ended up killing her in the schools storage room. Before we continue to talk about the murder Of Kim Ujin let's first get to know the two sisters and why Sara hated her younger sister so much. Ujin and Sara were both daughters of Koreas top 10 Tech COMPANY, CEO KIM HAN SHI, having being born with both a mother and father who are well off the girls never experienced a day where life was to hard for them unless it was their studies of course, Sara was Mr and Mrs Kim first child, It wasn't to hard taking care of her but at the same time when Sara was only 3 Ujin was born and that made it very difficult for her to get her parents attention. As they grew older they grew to secretly hate each other while putting up a show in front of their parents, but even though, Sara could tell that there was something off about Ujin and she wanted to know exactly what it was so she could blackmail her about it, but that investigation didn't go so well and at the end of all this fighting it turned out that Sara really did have a strong hatred for her sister meanwhile Ujin actually found it as a way for siblings to just tease each other. And then this is when we come to the day where Sara kills Kim Ujin