Dramas with a well-written maniac/killer

 fanitha:

Forget to mentiok: Kazoku Game, he is not a killer but he is some kind of maniac

Looks interesting as well!

 SylverWolf:

Sahsiyet (Turkish drama) - really good about a serial killer and detective looking for him

Thank you! Never watched Turkish dramas before, so maybe this one would be a good start :)