I often explained it, because many don't seem to get it - Edit 1
Before modification by Etzel at 20/11/2009 12:29:10 PM
Because it obviously would have a more powerful impact. If Graendal was the killer, BS just had the chance to reveal it in her PoV in TGS, prologue. Why then, should he skip this opportunity to let it e.g. Moridin tell someone else that Graendal did it? Makes no sense.
And if SLAYER were the killer (note that "were", not "was" is the correct subjunctive form here), why wouldn't he be more proud about that accomplishment than killing a couple of stupid Black Ajah Aes Sedai when it was HIS PoV??? It's funny how you use one argument to disregard one person while ignoring that same argument to favor another.
Isam & Luc obviously hate Aes Sedai for very personal reasons (in short: Isam is Malkieri, Luc was manipulated by AS). Therefore Slayer likes to kill AS best, of course especially in such a bloody way like it was possible in TSR. On the other hand, nothing suggests that Slayer hated Asmo that much, who was after all a former possible patron. It's rather ridiculous to believe that Slayer prefers to kill "more powerful people", as you seem to believe, since he also considers in his PoV that it's just "a pity" that he won't soon get another chance to kill the most powerful person in the world, Rand (and he still thinks about those AS as his best kill, while he is on his way to kill the DR, whom he just calls his nephew!).