He should be put in a place where society is safe from him, but where he's also safe from harm. Yes, it may seem unfair, since three of his victims will never be able to enjoy the same. But life doesn't allow us trades. We can't magically switch off his life and bring back even one of the dead victims. We can't torture him and magically have the injuries of one of the living victims disappear.
If we treat him like he's less than human, that he doesn't have the same rights under law that we do, if we torture and kill him for our amusement, then we are embracing a similar philosophy to him: we're just differing on who we're dehumanizing, and the degree of abuse we're committing against them.