Theories about who the Joker may be

 Toblie:

Ok Who is yeong-sim and why has she been mentioned a few times to Yong shik, to visit her and her dog? They were mentioned again in this ep 11 by the doctor. Have we seen them yet? Does the dog hold a clue or even her? Being mentioned at the beginning and now there has to be a reason.

As far as i can remember, Yong Shik hasn't visited that damn dog yet lmaooo So my suspicions are mostly on Yeong Sim now

1st Theory - 

The guy at the end of ep 11, was the who fixes her sink and installs CCTV, right?

Hyang Mi went with him to the house with red peppers in it. A third person was with them - that can be Yeong-Sim. Her dog might have died bcoz of some stray cats and that family decided to kill every cat in the neighborhood by adding pesticides with cat food. Pesticide from the doctor's comment when Yong Shik got the infection from the pesticide.

Plus the flour on shoes can the pesticides. Gloves with Joker to avoid the infection like Yong Shik. Coughing (when joker tried to kill Dong Baek for the first time in cosmetics shop) can be a side effect of pesticides).

Same scene - string with which Joker killed DB's friend is the same as the one with No Kyu Tae picked up when he was in the shop - the scene when Yong Shik analyses who all he met since the time he decided to install the CCTV in the bar.

The guy mentioned in the post ( https://kyoru.co.vu/post/188547575757/another-episode-and-still-have-no-idea-who-the) was drying the red peppers outside the house, however when Hyang Mi went to the house, she mentions that the floor was hot enough to dry the red peppers inside the house, so I don't think he is involved in any way.

Joker can be the one who at the end of ep 11 (the one with cat food bag) and his wife/sister/mother (the dress is shown just when the scene changes to Dong Baek's mother - moving from one female character to the next one) can be the cat killer.

2nd Theory - 

No Kyu Tae can the Joker. One of the trailers says DB meets 3 guys - Good/Bad/Cheap - Yong Shik is a good guy; NKT is bad (Joker) and Kang Jong Ryul as the cheap one (coming back to an ex just to avoid the current wife's nagging.

Every clue ending with NKT. Everyone kind of neglects him and tramples over him so he asks to stop being a joke to everyone he is angry at. For 5 years he was silent but when Yong Shik came into the life of DB, he became active.

Side story - 

DB's mom can be dying and trying to transfer the insurance money to her (when she is looking for her seal) OR is she trying to scam her own daughter?

Which theory seems like the actual case, please do comment.

Is the director of Hanbit academy - the father of Heung Sik - the one who got locked away by Heung Sik? (ep 12)

I kind of feel like it's someone we do know but at the same time we don't know their relationship to people. Think about everyone in Ongsan is basically related someway or another in their town right. So explaining who everyone is can be quite a bit.

I kind of feel like it maybe the father of the guy who put up the CCTV in Dongbaek's bar. Who his father is exactly I'm not entirely sure about that though. 

I'm think all this is too much suggestive to be Hyung Sik, in my mind, I believe this could be a trick to confuse us. In my point of view is too early to reveal the Joker.

I still believe the Joker is the baseball coach.
If the Joker is someone out of the regular characters, to me, don't will make much sense, like HS father, like some here are suggesting.

I guess the Joker is someone who has never raised suspicious about who he really is.

And to me Hyung Sik and No Kyu Tae  is out of question.

I think It is the handyman and his dad working together...think 1 starts the fires and the other does the murders 

The dad is mentally unstable talking about burning witches and there was a message on the bus related to that and he is old enough to be called "ahjussi" by Hyuang Mi and killing cats since witches like cats .  Plus DB's mom was a witness to the salon murder and confronts the handyman about seeing him enter the salon that night right before the murder and that he had access to the bar  

I also think that YM was attacked and hurt by several people...the exs wofe hit her with the car , the landlord's wife probably punched her, DB's mom went to get the money back she stole and hit her and got the bruises on her arm ( or tried to retrieve evidence that someone burned with YM's coat and got a burn) ....reminds me of Murder on the Orient Express with all suspects stabbing the victim

 Shay:

first of all a spoiler for people who didn't watch that.....but in that one it worked well.....what I'm saying is people get attached to romance really fast and so in this drama having all this developed romance only to have him be a criminal is U_U disappoint

I deleted the post with the spoiler since the old school spoiler tag didnt work and I finally figured out that it is now the triangle with exclamation point that hides spoilers so you can delete this too if you want since it still shows the spoiler