User blog comment:Krauserlols/Is Riven a real Wind Master?/@comment-9593635-20131219032003

I think that the most compelling argument against the killer being Riven was that the Elder was killed in an assassination, and Riven was a field commander. "Oh, hey, troops I'm commanding in this invasion, you guys just chill for a while on foreign land without orders or supervision; I'm gonna go do a thing real quick someplace pretty far away" ...said no commander ever.

Riven stayed in command of her unit until her desertion; she was fighting with them up until the moment that that happened, during the Zuanite bombardment. I think it's highly unlikely that the commander of the unit would AFK to go single-handedly perform an assassination. But maybe that's just me.