The phenomenon of patient homicides committed by health service employees has, in the previous years, repeatedly aroused much attention. The cases made known in Germany, the USA, Holland, Norway, and Austria appear to provide evidence to the effect that we are not only dealing with unique incidents. The scientific investigation of this especially sensitive taboo-topic is, to date, missing. The judicial trials carried out emphatically indicate that culprit motives, colleague behavior, but also to a large extent decisions made by superiors remain unclear. It remains controversial, what effect working conditions, strain of employees, their level of education and personal viewpoints over such criminal acts they possess. Finally, the long latency period between the first internal suspicions and the responsible parties' appropriate reactions requires duplicatable explanation. The following paper presents a German single-case study of patient homicide by a female nurse. The focus on causality rests on the presentation of developments up to the point where the long-fermenting suspicion could no longer be dismissed, and appropriate consequences took place. The account largely avoids the "definite" findings required during the judicial process. It concerns rather above all an open, uncertain, and possibly without external influence course of development which in stages each colleague in the health professions can trace, to the point where the uncertain and horrifying suspicion became a certainty. With this single-case study in hand it is made understandable in which ways personal circumstances and professional conditions at the worksituation can intertwine in such a way that the original motivation to help turns into its abysmal opposite. It is the author's intention to make preventive learning possible through this single case study. Every employee in the health professions should proceed on the assumption that such occurrences could also in his own field of work come to pass. In this respect, it is of considerable importance to differentiate between hasty and untenable incriminations and original increasing early-warning signs.