I have watched 8 episodes and I have questions regarding the end of episode 7.
JM's arrest: How did the 2 leads show up at the exact moment he dug out MJ's body? Dong Shik was adamant on making sure the killer is charged for the murders, upon finding out that MJ who was like a daughter to him was killed by her father/ his long-term friend, this man reined in the impulse to call it in and put on a cool facade because there was no body. Then what led to the decision to go arrest JM in 7th ep? He couldn't have known the body was in the house. Rashly arresting JM at that moment could have ruined his entire plan to prove his guilt.