There's an NSFL case that gives me nightmares. Google Fred and Rose West, a husband wife duo.
I can't fathom how two cruel and evil people came across each other and married.
BOTH parents graped and mutilated their 6-7 daughters, murdered several children for 20 years before getting caught. And the count is what they admitted to and found, it could be more. The mother alleges she herself was abused by her father previously.