Give us a little more to go on...can you prove that Padan Fain was in Camelyn at the time? Actually I have a reference from the end of TSR when Padan Fain makes the comment that he is going there after he gets his dagger from the White Tower. Develop it.

If Padan Fain did kill Asmodean, How? The wording of Asmodean's death is kind of strange for a person being killed by the Shadar Logoth Dagger. "The word still hung in the air as death took him." Sounds more like balefire to me.Also would Asmodean recognize Padan Fain. If you can answer this questions than I think Padan Fain is are assassin of Asmodean.