I love thrillers/murder mysteries and it's been a while since new psycho killer dramas. Kim Young Kwang with his jokerish smile was a great choice for this role and there's no question the whole cast can act but the weakness is in the script.  
The dialogue felt slow.

By Ep 6 I am just like what is this sloppy nonsense?  Literally poor decisions all around.

Why did disabled cop go meet him alone?
Why did she go party first before calling her colleague about discovering ...?
LGBT Shaman storyline felt random
ML and ML only shared a few lines and deeply connected?  There really should've been some development with that.
Overly dark lighting
Radom fingers on the phone screen...............

Lost potential with this great cast because there could've been so many interesting storylines:
ML back scar story?
FL first gambling hall employer?
FL and Cop friend, how were they able to grow close then fell apart at some point?
How did she become that way?
Shaman and cop, what's the story there?
FL & ML 's emotional connection at a deeper level?