Searching for Evidence

Whoever is behind the transformation of the spirits has been very deliberate in their actions, taking care to target the most powerful mages first, but why? The kind of magic required to influence the spirits of slain Kirin Tor mages must be very powerful. Why would a powerful mage go to all this trouble? I'm inclined to say this is another plot of Kael'thas's, designed to cause more misery here. If there are blood elves here, they're likely to be hiding in the houses across the covered bridge.