The reason I believe we do not have the right to kill someone is because it is inhumane.
While their actions may be inhumane I do not see why killing the perpetrator makes the sentence just and not just revenge.
I also don’t understand why the family of the victim would want the perpetrator killed for any other reason than revenge.
How can it be just to kill those that have killed?

I’ll throw the question back at you. Why do you think the death penalty is anything other than revenge?

Take Sutcliffe for example, if he had killed my mother, call it revenge if you want, I would be more than happy to kill him myself. Revenge? Justice? Call it what you will.