Okay . . . so I have a theory.
Mianite's four lived in a parallel universe, right?
So that means whatever happened there was happening in Ruxomar. (Bear with me if I don't make sense.)
Dianite died in s1 and s2. And who killed him? Syndicate, in the old world. That means his parallel killed Dianite now.
So, possibly, Mot_Screziato is Dianite's killer.
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This is just an idea. Let me know what you think in the comments :P Peace out