Serial killer dramas with nothing supernatural?

You must check out Hello Monster, it's excellently done.

Also watch Come & Hug Me. 

And if C-Dramas are your thing, Love Me If You Dare.  

Also I've only watched the first episode so far, but I'm pretty sure Flower Of Evil will fit the bill as well.

• +1 Hello Monster
• +1 Come and Hug Me
• The Smile Has Left Your Eyes
• Misty

Strangers from Hell

Voice

Stranger

Signal

Light on Series: The Bad Kids 

Not really about investigative work but involves serial killing, no supernatural stuff.

• Missing Noir M 
• Kill It 
• Criminal Minds

Been a while since I watched them all but I'm pretty sure there was a serial killer in them all.

-1 Hello Monster it's so boring... like seriously I read the synopsis expecting something great but nothing happens and it very lack-luster

+1 Come and Hug Me 

+1 Misty

-1 The Smile has Left Your Eyes but I recommend watching the original Japanese version One Million Stars Falling from the Sky as it's MUCH better with the acting. If you do watch it, don't read the synopsis as it will ruin it for you.

-1 Kill It it starts off strong but let me tell you, this is the messiest drama I think I  have EVER watched and actually completed. Anytime I see it being recommended I have to let people know not to waste your time.

Movies:

Monster

I Saw the Devil 

Bedevilled

Memoir of a Murderer