Do serial killers have super ego?

"super ego" is a Freudian concept. Freud saw the super ego as the part of the psyche that limits behavior to meet social norms. He would probably argue that serial killers have a weak or missing super ego.

That said, super ego was a purely hypothetical concept. Freud concocted the idea in an attempt to explain/understand the behavior of his patents. So there's no way of telling who has or doesn't have one.