"Manipulation of people is [her] primary aim"
-- Dr. Westbury after examining young Mary
At her trial, a psychiatrist who had examined Mary testified that she exhibited the classic symptoms of psychopathology (or sociopathology) by her lack of feeling toward others. "She showed no remorse whatsoever, no tears and no anxiety. She was completely unemotional about the whole affair and merely resentful at her detention," reported Dr. Orton. "I could see no real criminal motivation."
Mary's abusive mother, her genetic wild-card of a father, and physical damage likely incurred by the repetitive drug overdoses all contributed to her sociopathology. Her inability to bond with others in a loving manner was twisted into a bonding process based on violent aggression. Mary responded to others based on how she herself had been treated. When a mother is a source of fear for a child, some cope by developing protective mechanisms against the outside world, which, for the developing sociopath, is a constant threat. Of course, not all children raised in abusive situations become sociopaths. Genetic factors and neurological damage also play a role. If a child is subjected to all of these conditions, the forecast can be deadly.
She certainly showed no signs of being satiated after murdering Brian. She was violent toward animals, a chronic bed wetter until her adult years, and while she hadn't set fires, she did destroy property in her brief career as a murderer. Those familiar with these "triad" of symptoms that characterize serial killers will also recognize that she probably wouldn't have stopped killing if unapprehended. Mary preyed on victims weaker than herself, and after the murders interjected herself into the crime investigation.
"Living in a fantasy world" is fine for children, but for psychologically disturbed violent offenders, the phrase rings ominous. Mary and Norma fantasized about being criminals and escaping to Scotland. "We built it up and up until -- it now seems -- We kept hoping we'd be arrested and sent away," she said. "We never talked about anything except doing terrible things and being taken away."
Medical experts do not believe that sociopaths can be "cured." They are generally resistant to therapy, which Mary had proven to be throughout her incarceration. Some do speculate that aggressive tendencies quiet down with age. Perhaps Mary is better. We cannot know for sure.