It doesn't indeed. Jordan didn't intend to solve the mystery for a reason. The murder story will be boring and evem mundane, how the opportunity arose will be fairly irrelevant in the grander picture.

The more people try to tie it to important aspects of the plot, worldbuilding and characters, the further from the truth they propably get. There's no big Finn-mystery involving Lanfear behind it. There's no big TAR mystery involving Slayer and mysterious powers that prevent the DO from seizing soul (as if the DO would grant one of his servants a gift like that!).

The clues aside (that mostly eliminated the other credible suspects until only Graendal and unlikely ones like Mesaana remained), the fact Jordan had no use originally for a resolution to the murder, that he decided to give it to us only because the "mystery" has become famous among fans, speak for the "meh" scenarios, like Graendal having been there to gain spies near Rand (spies we know later she has here and there.. and that's all that was important to know, that she kept herself well-informed) and bumping into Asmodean by accident. Irrelevant to the rest of the story, and a tad boring - that and the fact Jordan liked not to have us understand too much what his characters have no chance to ever learn about explains well why this wasn't on his priority list of things to resolve. Asmodean's murder wasn't a mystery, it was a plot device to a) get rid of him before the BT story arc, and b) give one more reason to Rand to be paranoid, something RJ intended to play on a lot in LOC.