The issue is figuring it out between those back two. Omni is knocking HARD on that WIFOM door for "why are the doc and cop still alive." I hate it. A lot. And it would explain the motive for the weird kills.Brosuke was still alive D2 when you both claimed so he could have told his buddy the plan they follow it after seeing what it could do.
You are right! There has to be an RB due to RR dying N2 when Felipe protected him but did not get a result so in that sense if there is a RB mafia member it cannot be Felipe/Ryker/Soup at all. So it is really between Inferno/Bardull/Omni.
So I think it is Bardull>Inferno>Omni.
Bardull has NOTHING redeeming and is probably the guy.