The Perfect Murder

8

Based on the information the three know currently is that Mr. Unknown leaves no blind spots and eliminates anyone and everyone who tries to get close to the truth or even gets involved with this. 

The next day, Yeesul went to the computer lab to finish her assignment which was due the day later. She ran all the commands on the school computer, but somehow those commands always showed an error. She checked over her book and made sure that what she was doing was correct. And to her surprise every single command she ran was correct, so how was she getting an error each time? 

Yeesul got up from her seat, visibly frustrated, and intended to call someone for help. The moment she started walking the computer blacked out. Yeesul got alarmed and checked if the PC was alright by tapping on the top of it for a bit. It was a code, encrypted in binary digits. Luckily Yeesul understood binary and jotted down the code to decrypt it. After a minute and a half, the display completely shut down. 

Yeesul grabbed her pen identifying the code written and found out this:

I'll make it easy for you, my next kill will be tomorrow. 
If you can find Ji Hee by then, I will postpone the kill to next week
- Mr. Unknown

"Oh no," Yeesul mumbled. Ara was the only one who knew but now that she's dead they need to find another alternative. Yeesul quickly called up Hyunwoo and Yuna and informed them about the situation.

"Wait, I remember Ara saying that Seolhee's father is still alive," Yuna said 

"Yes, but his location is unknown" Hyunwoo reasoned 

"According to the background research I did on Seolhee, someone else resides in her house currently and that the Kims sold their house to the current owners," Yuna said

"So if we ask them, maybe we'll get some intel?" Yeesul asked

"Precisely" Yuna replied 

It was a 15-minute drive to Seolhee's house. It was a fairly average house but looked really bright because of the flowers decorated around the house. An old couple resides in that house at the moment. They are known around town for being kind and humble. Yeesul knocked on the brown wooden door. 

"May I help you?" A young woman asked, which took our ravens by surprise since she did not look old at all

"Y-yes, are you perhaps Mrs. Cha Hyejin?" Hyunwoo asked

"Do I look that old to you?" The blondie joked 

"And no, I am not Cha Hyejin. She's my mother" The lady chuckled 

"I am Cha Anna, may I ask what work you have with my mother?" She asked

"I am Kim Yuna, she's Choi Yeesul and he's Kwan Hyunwoo. We're here to ask about the previous residents of this house" Yuna politely stated 

"Well then, be my guest," Anna said 

"Who is it, Anna?" An elderly lady asked who must be Mrs. Cha

"They'd like to have a word with you" Anna stated and left the three alone with Mrs. Cha

"Hello, Mrs. Cha,  I am Kwan Hyunwoo, they both are Choi Yeesul and Kim Yuna," Hyunwoo said

"We're from Seoul University and we're here to ask you about the previous residents here" Hyunwoo added

"Ah well, I do not know a lot about them but all I know is that he's out of country," Mrs. Cha said and the three's faces were visibly disappointed 

"I am sorry my loves, here take some cookies on your way. Maybe that'd help cheer you up" Mrs. Cha said and handed them a basket of different shaped cookies

 Soon Yeesul received a call from her mother. She had some urgent business to deal with. "Let's meet up at the park at 6 PM," Hyunwoo said and the others agreed