Vergottini said Van Heerden displayed strange behaviour, even as a young girl.
When her mother told her that dolls come alive at night, Van Heerden blindfolded her own dolls and bound them with shoe laces, said Vergottini.
Van Heerden's meeting with her co-accused Van der Merwe led to a disastrous partnership.
"They together [in a relationship] are a disaster. It created a platform for their behaviour," Vergottini said.
Van der Merwe was diagnosed with schizophrenia at the age of 14.
Vergottini said when Van Heerden and Van der Merwe met, they discovered they both had fantasies that were not normal to the rest of the world.
The couple watched the television series Dexter, in which a serial killer is the hero, reading it as condonation for their own activities.
One of the old urban legends floating around the occult community here in America is that magicians who are careless or practice improperly run the risk of developing mental illness. I put up a post on this topic back in 2007 and the reason I say urban legend is that I've become more and more convinced over the years that it simply is not true.