The investigation showed that in 17 out of 75 cases no causal relationship between the illness and the criminal act was deemed to exist, which may mean that the medical principle results in impunity in a considerable number of cases in which the perpetrator’s mental health has had no effect on the criminal act. The absence of a causal relationship between psychotic disorders and criminal acts was found also by Taylor in 1985 (9). She found that 43 % of a sample of psychotic perpetrators ascribed their criminal acts to psychotically motivated causes.
Homicides were clearly more likely to be deemed psychotically motivated than to be considered to have no causal relationship to the defendant’s psychosis. This finding is consistent with a number of studies that indicate an increased risk of violence for psychoses in general and a correlation between psychosis and homicide in particular (10) – (12). A major review article by Taylor from 2008 (13) concludes that in the most seriously violent persons with psychosis, the violent behaviour is most often motivated by the psychotic symptoms.
Group 2 also had a larger proportion of charges for possession and use of drugs than Group 1. This finding is also consistent with Taylor’s study (9), in which only 29 % of the less serious crimes were deemed to be related to psychotic symptoms (delusions) in the perpetrator. A similar tendency was found for crimes against property, in that such crimes figured more frequently in Group 2.
As can be seen, the causal relationship between the illness and the acts is elucidated by investigating the charges, rather than the perpetrator. This choice is justified by reference to the focus on the correlation between the illness and the act. It is the defendant’s state of mind at the time of the act that will be considered in determining legal insanity. However, several defendants had been charged with multiple felonies, and some of the rulings failed to state clearly whether separate psychiatric assessments had been undertaken for the different times of the criminal acts. This uncertainty represents a weakness in our study.
At the same time, this illustrates a highly relevant topic in forensic psychiatry, since a psychotic criminal may commit numerous felonies for which he is exempt from penalty, although not all these acts will necessarily be motivated by delusions or in other ways result from his disorder.
Our study presumes that it is possible to assess whether a causal relationship between a psychotic state of mind and a criminal act exists or not. However, the authors of the public reports that form the basis for current legal practice – that follow the medical principle (1, 14, 15) – have questioned whether this is feasible. The public reports state that a psychosis that renders the defendant legally insane affects the entire personality, and there will thus always be a risk that the act is a result of the mental disorder. Excluding a causal relationship between the psychosis and the act will be fraught with a great deal of uncertainty, and this will entail a considerable risk of a wrongful conviction (16).
In addition, our study is based on a material that has not been produced for the purpose of drawing conclusions regarding a possible causal relationship between disorders and acts. A statement by a judge that the act was «deliberate and wilful» is not in itself evidence that the act was not influenced by the psychosis. A retrospective assessment of whether a perpetrator had a clear understanding of his acts or whether these were linked to his mental disorder must of necessity be a subjective judgement. In making such an assessment there will normally be no objective observations to rely on for support.
It deserves mention, though, that the measurement of inter-rater reliability in the assessment of correlations in the present sample revealed a marked consistency. The consistency was not perfect, however, since there was some disagreement between the raters.
The investigated data set consisted of 75 cases and encompassed rulings made over a period of 18 years (1994 – 2012). Cases that did not fulfil the inclusion criteria regarding application of the law or the level of detail in the legal text were excluded – altogether 298 rulings. The sample size is relatively small in relation to the number of defendants who are declared unfit to plead on the grounds of psychosis pursuant to Section 44 of the General Civil Penal Code. During the period of 2007 – 11 alone, there were 366 expert reports that declared a defendant to be psychotic (17).
The reason why only a minority of these cases were available for inclusion in the present study is most likely that a majority of the less serious cases involving Section 44 are dismissed by the prosecuting authority (18). As a result, the sample represents the most serious cases in which a defendant has been found legally insane. This implies that the representativeness of the sample is limited, provided that the purpose of the study had been to generalise the findings to all criminals who are found not guilty by reason of insanity.
Another weakness that deserves mention is that the empirical basis of the study has been retrieved from a dynamic online database which is constantly changing, and this means that the search cannot be identically replicated.
Despite these weaknesses, many of the study’s findings are consistent with those from scientific inquiries that have used a more suitable methodology (9, 13). The Norwegian criteria that are applied for declaring a person legally insane have been widely discussed on a theoretical basis. However, only few empirical studies are available regarding the characteristics of those who in fact have been found not guilty by reason of insanity.
In our opinion, it would be useful to continue undertaking more thorough studies on this topic. It would also be desirable to explore whether practices for declaring defendants legally insane have changed over time, since our material is too small to draw any conclusions in this respect.