"Im not one to lie. Nor do I kill without reason. - Salma, succubus
The witcher's investigation uncovered that a succubus named Salma was responsible for the string of killings afflicting the Novigrad city guard. This came as a surprise, for succubi do not usually commit premediated, cold-blooded murder. This is not to say they are not dangerous: they will at times kill on accident, when carried away on a particularly gushing stream of ectasy. At other times, they kill in self-defense: though they have the look of slender maids from the waist up, their supple limbs hide incredible strength. They present witchers with an intractable dilemma: does this monster, who wishes men no ill yet all the same often cuases harm, deserve death, or mercy?
That is exactly the perplexing question faced by Geralt of Rivia. In the end he believed Salma and decided to let her go free - though he could not shake off the feeling that he might live to regret that decision."
- It's not necessary to kill her. Geralt can talk to her and decide to let her go. She will give a nice sword and proof for guard in reward. The consequences though are to be discovered by Geralt later in game.