Criminal love

Hyunjin is a detective and he's currently working on solving a murder case. He has ruled out the three suspects: Han Jisung, Male, 23 years old, Korean. Lee Felix, Male, 23 years old, Korean. Lee Know, Male, 24 years old, Korean. He goes undercover and talks to the three as a friend rather than a detective. He gains their trust and there's nothing un-ordinary about Han and Lee Know, but there's something about Felix... something odd but fascinating...