Dragonmount reported from a recent signing the following Q&A:

Q: "Were you surprised when you found out who killed Asmodean?"

A: "Brandon had been a fan for a long time before he got to find out who killed Asmodean. He said that he had heard arguments for every possible suspect, including the really crazy ones like Tam. So when he found out the real answer, he wasn’t shocked. His reaction was more 'Oh, those guys were right'. He said that the clues are there, but he never would have figured it out himself."

This surprise ("Oh, those guys were right" ) clearly speaks against the idea that the "obvious" suspect of the majority of the WoT fans, Graendal, killed Asmo. Of course, Graendal's death already made it most unlikely.

And btw, Tam is apparently also excluded..