"There is no instrument that is specifically useful or validated for identifying potential school shooters or mass murderers,” Stephen D. Hart, a psychologist at Simon Fraser University in Vancouver who is the co-author of a widely used evaluation tool. told the Washington Post. “There are many things in life where we have an inadequate evidence base, and this is one of them.”
Even when someone has a history of threatening behavior, the killing of innocent
people can’t necessarily be prevented.
The task of identifying violence-prone individuals is even trickier with
young people, who have shorter histories and whose normal development often
includes a period of antisocial behavior.
Psychologists and psychiatrists have been working for decades to try to
figure out whether there’s a link between mental illness and violence, and if
so, which people are likely to act. Using an ever-changing tool kit of theories
and questionnaires, they’ve made some progress, according to the Post.
It’s now fairly clear, for example, that people with severe mental illness,
such as schizophrenia, bipolar disorder and some personality disorders, are more
likely to commit violent acts than others. But the risk is small. The vast
majority of mentally ill people won’t commit assault, rape, arson or homicide,
although the risk rises sharply among those who abuse drugs and alcohol.
To read more: http://www.washingtonpost.com/national/health-science/predicting-violence-is-a-work-in-progress/2013/01/03/2e8955b8-5371-11e2-a613-ec8d394535c6_story.html?hpid=z2