Really? i dont think so. it will be swain and leblanc. Reread their judgements and then read cassiopia's judgement and the new JoJ.
in their judgements, swain said he was going to rule and that he hated General Du Couteu (or however u spell it.) who is cassiopia's father. Then he is kidnapped and there are no leads.
in swain's judgement, he said he wants to rule. To do that, darkwill needs to go. In LeBlanc's judgement, swain and LeBlanc state that they both hate darkwill and want him to pay. What he is paying for isn't said. And now, Darkwill is assassinated and demacia is blamed. Which is exactly what they both want: Darkwill gone and war & violence with demacia.
Its so obvious. Swain and LeBlanc, and through her the Black Rose, assassinated Darkwill and are blaming Demacia for it so that noxus gains the kalamanda mining rights and so that Demacia suffers and maybe punished by the league.
Yes, I'm sending this into the JoJ crew.