There is also a comment from Moridin about it. - Edit 1
Before modification by darius_sedai at 16/07/2011 01:45:39 AM
I don't have the book in front of me, but although Shadar Haran didn't say it outright, he said Graendal killed 3 Forsaken, and the obvious one, Aran'gar, and thinking about the second one, Mesaana, there's only one unaccounted one left: Asmodean. Sanderson just blatantly put it in for the people that didn't find the tidbit.
He asks her if Aran'gar was also a traitor, and notes that she seems to be making a habit of killing other Chosen.