For the study in the scientific magazine ‘Forskning och Framsteg‘ — which has also been published by The American Journal of Psychiatry — researchers examined the court psychiatry records and other medical evidence for 2,000 people found guilty of murder, attempted murder, manslaughter or attempted manslaughter between 1998 and 2001 in Sweden.
The certified psychiatric illnesses include schizophrenia, personality disorders, anxiety, post-traumatic stress and depression.
…The Swedish situation is different from that in countries where organized crime, drug trade and easy access to weapons result in a higher percentage of murders committed by people who are not certifiably ill than in Western Europe, the study’s authors acknowledged. They cited as examples the United States, Bolivia, South Africa and the Baltic countries.” (Yahoo! News)
When psychiatric evaluations are done through the court mental health services, of course, diagnoses are arrived at with full knowledge of the crime the subject has committed. Arguably, this makes finding a “certified” psychiatric diagnosis more likely. Furthermore, some of the diagnosed conditions are personality disorders. One of these, antisocial personality disorder, has among its DSM-IV diagnostic criteria aggressiveness, reckless disregard for the safety of others, and remorselessness over mistreatment of others. (I like the ICD-10 criteria better, BTW.) It may be a bit of circular reasoning to diagnose many murderers with antisocial personality disorder.