What happens when the assassin is a mage and does “take control” of his victim with a spell like Charm or Hellbind Heart ?
The victim switches sides, followed by a “there was a battle” message showing him fighting his previous friends. Double damage. Plus if he was the last commander he gets to watch his previous troops go bye-bye (rout from the fight) and gives you the province and any items/gems he might have had (but even a militia leader will prevent the rout).