If you mean... - Edit 1
Before modification by Etzel at 29/12/2009 04:03:20 PM
I would say Graendal's POVs might already contain confirmation of this - but others have already pointed this out in detail, so I'll just refer you to Theoryland.
By this apparent "confirmation" in Graendal's PoV that she seems sure that Asmo is dead, then you fall for a common misunderstanding. This doesn't mean at all that Graendal is the killer. For example, she might simply learned about Asmo's death from the DO like Demandred did (or maybe she even learned it from Demandred), or she could simply be the Forsaken, who sent Slayer.
Masema has had more of a role in the series than Slayer has, and his storyline ended in a rather one-note fashion. So I'm still not convinced. In fact, given that Slayer has more to do with Perrin's story than Rand's, leads me to believe that this is an enemy that Perrin will need to confront, and Slayer may have nothing to do with the Forsaken or the other characters.
Well, I definitely would disagree that Masema was a more important character than Slayer is. However, the fact that Slayer will likely eventually be killed in the next books, doesn't rule him out as being Asmo's killer (by the way, wasn't this your argument regarding Graendal?), at least if he has a PoV before his death, where the deed is revealed.
Furthermore, we already saw Slayer dealing with Forsaken and trying to kill Rand, Nynaeve, Fain and others. Therefore you argument about Perrin doesn't make much sense, especially since this future role also wouldn't rule out that Slayer killed Asmo before.
And you're description of him dovetails exactly into why I find him and the theories about him so unconvincing: they all revolve around "His name is Slayer, which means he's deadly! And he has powers in T'A'R!"
By the way, we have absolutely no evidence that his powers are derived from the True Power. Firstly, it is possible for non-channelers to be Dreamers. Secondly, the Dark One can transmigrate souls, merge bodies/souls and affect the Pattern - all without using the True Power. We have no reason to believe the True Power is anything but a parallel force of the One Power that only channelers can access. Lastly, his powers in TAR seem to be less than that of a master Dreamer or Wise One - it looks like the only thing he does is enter it in the flesh. It is unknown if he can pull others into the dreamworld or etc.
We know from RJ, BS and Slayer's PoV that Slayer got several gifts from the DO. How else should the DO grant these gifts, if not by the TP? Also Shadowspawn like Myrddraal or former humans like the Gray Men have "channeler-like" powers (e.g. a kind of Traveling or the ability to be invisible), which ultimately must stem from the DO, and thus the TP. It's ridiculous to believe that the DO gave Slayer unimportant gifts, since he obviously wanted to create a top assassin.