There is only one person who can remove Cain’s mark and let him die – Dr. Linda.
It’s been stated before that Lucifer doesn’t send people to Hell or hold them there. It’s solely their own guilt. What if it’s no different for Cain? What if over the centuries he’s never really forgiven himself for killing his brother? Cain’s mark is an external representation of his internal guilt. If he can truly let go of it, he can leave his Hell on Earth. And who is the one person who can help him do that? Dr. Linda.
by Nymaz – View Source