Its actualy kinda interesting. I took the second part of my psychology final today and it included a case study similar to this. a 12 year old gurl would molest her younger brother (age 10), Threaten to kill him, would squashe baby birds hide knives, mastrobate five times a day publicly. Her parents were both ministers raised another kid perfectly well, but nomater what they did this girl at that age was that violent and that sexually perverted.
I think a case such as this is probobly not the parents fault I would assume some sort of social disorder?