During the genocide in Rwanda, about 800.000 - 1 million people were killed during 100 days by at least 120,000 perpetrators. From a social psychological point of view, it has been described how a process changes ordinary people into those who start committing evil acts. There is a general choice for all of us between concern and cruelty. But there are also more-or-less hidden factors predisposing for one of the choices. What makes us resistant and what turns us into passive bystanders or perpetrators? Social psychologists distinguish between constructive or blind patriots with more-or-less autonomous selves. Our oscillations between depressive and paranoid positions determine the establishment of open and closed minds. After two visits to Rwanda and via analysis of interviews with perpetrators, I will present a model of understanding decisive factors in the choice of becoming a perpetrator. In the model, uncontrolled prejudices are perverted via a phenomenon, that I call vertical relationships, into a closed system without tolerance of differences, ambiguities and uncertainties.