Sources

Psychohistory
Ever since the end of the Second World War, Hitler and the main Nazi leaders have defied the scientific community: how does one explain the psychology of politicians responsible for the worst atrocities and showing no remorse for their actions? Psychohistory, the discipline that combines psychology and history, posited the existence of a direct correlation between the intensity of the Nazi extremists’ psychological disturbances and the intensity of their cruelty (Friedländer, 1978). But such a model cannot be generalised. Many patients suffering from severe mental disorders do not show any sign of violence towards their environment.
Consequently, I put forward the hypothesis that the intensity of the mental health disturbances of any individual resorting to extreme violence is merely indicative of the socialisation of the violence used (Cotter, 2006). In this model, political crime, as represented by Hitler and other Nazi leaders, is associated with low intensity psychological problems (Browning, 1992). Suffering from mild symptoms, Nazi extremists were able to rationalise extreme violence and construct an ideology, disseminated amongst members of targeted groups. On the other hand, in contact crime (where there is physical contact between aggressor and victim, e.g. serial killers), individuals are affected by psychological disorders so severe that they are incapable of building a complex Weltanschauung (a theory of the world) (Jäckel, 1972) to vindicate their use of violence.

The authoritarian personality
In the review of references consulted, the study on the authoritarian personality by Theodor Adorno, Else Frenkel-Brunswick, Daniel Levinson and Nevitt Sanford, published in 1950, must be mentioned in second place (Adorno et al., 1969). The Berkeley group arrived at the conclusion that there are certain characteristics common to every person receptive to fascist propaganda. These people, it was postulated, must have the same mental structure, described as ethnocentric and prone to prejudice. The authoritarian mental structure is contrasted with the liberal one, which is defined by the opposite characteristics, i.e. non-ethnocentric, unprejudiced and unreceptive to fascist propaganda.

Psychopathy
In 1941, a few years before the publication of the Berkeley group's findings, American psychologist Hervey Cleckley had given a detailed listing of the characteristics of the psychopath, the most striking of these being the lack of remorse in the use of cruelty (Cleckley, 1988). A psychopath has a very egocentric view of the world and distorts reality in order to justify his actions. Following in Hervey Cleckley's footsteps, Robert Hare compiled in the 1980s a list of twenty indicators identifying psychopaths and measuring the intensity of their symptoms (Hare, 1991). It will become apparent below that both concepts – Hervey Cleckley's psychopathy and the Berkeley group's authoritarian personality as seen above – are combined in the psychopathic aggressor, the personality type common to all forms of extreme violence.

FBI research
In the 1970s and 1980s, several FBI agents (the celebrated profilers) carried out research on murderers acting repeatedly and in isolation, without any apparent ideological motivation. They split them into two categories: organised serial killers, who plan the execution of each crime, and disorganised serial killers, who act on impulse and are incapable of controlling their actions (Hazelwood and Douglas, 1980). Both groups are characterised by a total lack of remorse towards their victims, and by their disregard for material gain: they are not seeking financial benefit, but look only to obtain some degree of emotional satisfaction.
The explanations developed so far can be used to start answering the questions surrounding the serial killer's enigmatic behaviour. We know, from the absence of ideological framework, that he suffers from acute psychological disturbances which prevent him from socialising his violence, unlike political criminals, such as the Nazi leaders. These intense difficulties constitute the first level of a serial killer's mental structure. On the second level, organising the chaos, is a rigid authoritarian personality which enables him to find emotional compensation for his internal disorders through violence. It is easy to understand that such a mental structure, in itself complex, would take years to develop, in most cases from childhood, as FBI agent Robert Ressler remarked: “Let me state unequivocally that there is no such thing as the person who at age thirty-five suddenly changes from being perfectly normal and erupts into totally evil, disruptive, murderous behaviour. The behaviours that are precursors to murder have been present and developing in that person's life for a long, long time – since childhood.” (Ressler and Schachtman, 1992, p. 116).