spinzgirl:
Dongbaek isn't her real name most likely, and the mother refers to Pil-gu as Dongbaek. So what if she also had a son she abandoned and he's the killer? It would explain her mother's bizarre behavior of running off randomly, as well as her comment in episode 8 about dark thoughts. It would also explain how Dongbaek was saved by the fire alarm, and why her mother's footprints were also at the scene of the murder. So most likely it's someone older than Donbaek by a few years I'd guess.
yeah seems the plausible after the recent ep, those are also the first thing to pop on my mind. it would explain why she is seemingly faking her dementia and those cryptic things she said. seems like she know (or at least has a hint) who the joker is but refrain from saying so and even faking her illness in fear of her life. beside (maybe) another kid there is also husband possibility (has he ever been mentioned yet??). that would also match the dongbaek unlucky narrative.
edit : oh someone mentioned it already
haruny:
Since it's very likely that Dong Baek's mother is involved somehow with the Joker too. What if it's her husband aka Dong Baek's father? We dont really know anything about her dad, at least I dont remember him being mentioned. He could also be the reason her mother had to abandon her, so that Dong Baek wouldn't get involved with her psycho/murderer dad?
seems possible