monfernova

The guy on the phone sounds young, probably a relative of a victim or falsely accused prisoner. My bet is on rookie cop cos he's such a big name. and his obsession with the ML would still fit. No other susses really, briefly thought ML's son-in-law, but I dismissed it

Maybe she hates him for forgetting and abandoning her or something, maybe her morals became twisted after what was done to her (probably raped and beaten and left for dead was the implication)

Some really interesting theories for ep 7/8 - I am thinking:

a) The kid in the flashback / no. 13 is NOT RSJ. He IS the killer. For some reason, RSJ is attached to the Yoon Jae identity, but that doesn't mean he is Yoon Jae. Maybe his PTSD scrambled up his sense of self and he attached to being one of the other boys. So I think Yoon Jae is the killer, but that RSJ is not Yoon Jae. Hell maybe he's actually the older protective one - I still hold that SH/Judge is *not* from the orphanage. I don't really know why he went to the scene of the third crime, but I think both brothers remain innocent. If he is the older protective one maybe YJ/13 is getting revenge for what he sees as neglect and abandonment by RSJ. He doesn't know RSJ is amnesiac.
b) Kid in flashback is Charles. He seems the youngest of the lot in both senses, and him framing RSJ is a twisted "payback" for kinda being the real Charle's replacement as son for the restaurant owner (maybe he knows who is mother is and sees RSJ as replacing him and sees it as unfair - the killer is also a brat who targets innocents to make the guilty suffer.
c) CRACKPOT THEORY - the killer is RSJ's blood sister. Her "dying" felt a bit unreliable narratory, and although yes, the pendant was on the bones, there are clearly 3 pendants already between the two boys and her, and the killer noticeable has a shorter stature. When we got a close up as they injected RSJ, they actually seemed to walk quite elegantly and with poise. So maybe?

Unrelated - how does Eun Ki fit in???? Maybe she doesn't. Maybe she was the one "outside" plant/ one un-planted juror, to allow for someone completely isolated from the innocent but lightly linked (Crazy Dog knows her mother who most likely sheltered YJ/13/NOT-RSJ and her mother is instead of giving RSJ a 2nd chance, possibly enabled the monster that is 13 to enact their revenge and more). Maybe she's like the Ultimate Hope/Viewpoint Character - the external wild card and force o goodness that will tip the scales towards the good guys.

I really like this show. Can it be dumb? Yeah for sure. Like why is RSJ casually investigating without a care in the world and in broad daylight? How was he not caught - lmao.

Very interesting! I'm really getting into this one now

So, if we assume there are multiple killers my suspect pool is:

Crazy Dog's assistant: He is acting "evil" but is actually taking revenge for the children? See hey na na nah comment below
Various jurors - japanese-style chef, sweet engineer, taxi driver, limping man or eun-ki - all have stake in this somehow, for the first two i think they could be other kids at the orphanage - someone mentioned below the murderer might not even know they're framing SJ as they genuinely think he's dead, not adopted, and thus taking revenge and "killing in his name". Sweet engineer particularly continues to be sus, he reacted to the scared of dogs comment. taxi driver and eun ki don't fit the bill for orphanage, but taxi driver could be messing around or trying to expose the orphanage guards, and eun ki might just want revenge *somehow* with a very childlike innocence view of justice. Limping man seems very likely, he is one of the kids most likely the one who fell from the bridge in ep 1 flashback, and wanting revenge for yoon jae etc.
Various police officers - IN PARTICULAR - either SJ's boss or his kind friend. It would be quite the twist and they would have the means to dig into his background and "take revenge" for him so he doesn't have to. Clearly, he's PTSD'd his past away.

Lastly someone mentioned it has to be someone on the judicial system who rigged the votes. My last guess is it is SJ/SH's father, the Scolding Judge. Ever unassuming, he is using his connections to take revenge for his children. But SH doesn't seem adopted so was he truly ever at the orphanage at all? I now think it was the "older kid" who always protected SJ who is the killer, and that is not SH.

In the case where it is the judge then, I hope they reveal it sooner rather than later. He's a bastard for using his "brother" in such a way, when he is loved and respected and his brother is already lonely and unwanted.

To clarify, I think it is one of the jurors, who grew up with both Male Leads and is framing them both in some way. All that confuses me is how the FL will play into this

Not necessarily. If they can frame one person, they can also frame the other. Think about it...