Phoenix, you wrote nonsense about the Salamander bandits. Reread the role descriptions and you'll understand why it was Necropolis who was killing.
I carefully read the description of the roles. Both Salamanders and Necropolis could have been the killers, but the cruelty and growth indicate the leader of the Salamanders.
Quote about the leader of the Salamanders?
A rogue mage from Zerrikannia. He was expelled from his order for excessive cruelty and an addiction to drugs. He led the attack on Kaer Morhen to seize the secrets of the witchers, to serve his inhumane experiments. The leader of a criminal organization known as the Salamanders.
Of course, I might be wrong, but if Necropolis killed both times, then he is definitely from the Salamanders; it's hard to believe that the Salamanders could have ended up in a self-defense situation twice.