This article reviews current developments in psychiatric assessment of sex offenders for criminal courts. These developments are characterized by constantly changing laws and increasing neurobiological findings about paraphilias. Psychiatrists must prepare their reports taking into account the tension between psychopathological, neurobiological, and normative aspects of their judgement. The complexity of such assessments can best be demonstrated by narratives. This narrative concerns a 47-year-old patient who killed eight women after strangling them and masturbating or having intercourse with the unconscious victims. He explained in detail six of these crimes and gave ample information about his history, sexual development, fantasies, and a number of other sexual crimes he had committed. From this information a plausible explanation of his development to sexual fetishism and from there to sadism could be derived. Brain MRI displayed gliotic scars in the frontal lobe and right hippocampus. Consequences of the various findings on psychiatric assessment of legal culpability are discussed in this paper, concluding that a differentiated approach to the assessment is possible only from a psychopathological point of view in which behaviour, clinical features, and motivations are analysed.