1.4.09: Who killed Adeleas and Ispan? --Revised
After months of investigation by Vandene into who the hidden traitor was in the midst of Elayne’s group, the answer gets handed to them in KoD when they make their near disastrous raid on a Darkfriend safehouse. "If you are going to kill them," Marillan said as if discussing the price of bread, "spare Careane. She is one of us." [KoD: 31, House on Full Moon Street]
It seems likely that Careane murdered Adeleas either to prevent her from revealing something learned from her interrogation of Ispan, or to simply get rid of a witness. The murders have the added benefit of sowing chaos and confusion among Elayne's group.