Contrary to most, I don't think that Asmodean's death was completely revealed in ToM. We still don't know for sure, who killed him.

Actually we just learned that Graendal was involved, namely that she was "responsible" for his death, like she was responsible for the deaths of Mesaana and Aran'gar (both weren't directly killed by Graendal, though). Since Graendal again shows in ToM that she likes to stay in the background, it's still more likely that she was responsible for killing Asmo by sending Slayer to do it.

I predict that we will get a Slayer PoV in the next book, where it is actually revealed how Asmo was killed. We still don't know the specifics, though RJ wrote an extensive note about the murder. Otherwise one can only say that RJ lied that the majority of fans got it wrong, which doesn't seem likely.