Still, why apparitions? It's rather specific. And the Sidar are good at keeping secrets, so he might not have learned all that much about them yet - hell, maybe he specifically wanted to lure, catch and interrogate one. Plus, he did apparently know what to do with the Divided Soul, or at least figured it out quickly enough. Maybe he didn't know for sure that this assassin was a Divided Soul and not anyone else that might want to kill a general in a dark fantasy world during a military campaign.