Characteristics of successful and unsuccessful insanity pleas

Thirty men acquitted not guilty by reason of insanity (NGRI) were matched on type of violent crime and compared to 30 men who unsuccessfully raised the insanity defense. Demographic, legal process, and psychological variables were compared. Eighty percent of successful acquittees previously had been found incompetent to stand trial, compared to only 33% of those found guilty and sentenced to prison. Ninety-six percent of NGRI acquittees opted for trial before a judge rather than a jury; 76% of cases raising an unsuccessful defense were heard in front of a jury. Unsuccessful attemptees also had significantly higher IQ scores and personality profiles characterized by acting-out potential and intact reality testing compared to profiles of NGRIs. The ability of the legal system to identify those meeting criteria for the insanity defense is discussed.