by Stephen Lally

About the author: Stephen Lally is a clinical psychologist and serves on the faculty of the American School of Professional Psychology in Rosslyn, Virginia.

As a forensic psychologist, I am often asked to evaluate men and women accused of committing crimes in order to assess their competency and whether they can be held criminally responsible for their acts. The law sets fairly straightforward standards for criminal responsibility, and usually I have little difficulty in deciding whether an accused individual qualifies for the insanity defense.

Thus, I’m often struck by the public outcry accompanying a high-profile trial that raises the question of whether the defendant was legally sane when he or she committed the crime. Each time, there is the same focus on the possibility that the perpetrator might be...