British Maniac Patrick Mackay
It's one thing to know the details of cases involving multiple murder, and it's another to be able to distill from them the prognostic red flags. At least this is clear: we do not yet know what particular behaviors predict that someone will become a repeat killer. We can only say that some behaviors are associated with these incidents more than others, and they can be linked to a collection of factors that appear to be statistically significant in risk assessment studies.
Many repeat killers behaved in ways that, in retrospect, indicated that one day they might act out — an inability to deal with stress, for example, and angry outbursts or retaliations against others. The unrelenting buildup of frustration appears to derive from the way they learned (or did not learn) to manage anger and stress. In essence, that's related to how their observations of role models interact with their individual cognitive processing. Those who experience higher exposure to violence in the environment appear to have a greater tendency to duplicate it.
Among developmental factors associated with violence are harmful substances ingested by mothers during pregnancy, chronic maternal stress during pregnancy, early maternal rejection or abuse, nutritional deficiencies, a low verbal IQ, and chronic trouble with attention deficit and hyperactivity. While no factor clearly causes it, in certain combinations and with certain dispositions, they can provoke anger, thwart the development of anger management skills, and trigger impulsive violence against self or others. If kids fail to connect early with caregivers, there can be problems later in life. In addition, self-worth, resilience, intelligence, and empathy are essential to building character for effective conflict resolution. Without these skills, children cannot establish rewarding relationships with community systems.
Among the specific traits or behaviors that signal concern, which we can see in the Mackay case, are his preoccupation with themes of violence, his low frustration tolerance, stressors on his family unit since childhood, the way he collected perceived injustices and blamed others for his issues, his ability to dehumanize others, his poor coping skills, his sense of superiority, his substance abuse, and his mental instability.
Those psychologists or psychiatrists who did issue warnings clearly spotted these signals, but others with more power over the decision-making process perhaps weighed other factors more heavily. In any event, Mackay may have been stopped somewhere along the way before three (or more) people were murdered. A system that allows this to happen needs to police itself and make a plan for improvement.