The post-conviction preventive detention has been consistently tightened in recent years. From a constitutional perspective, this is problematic. Additionally, questions arise about why a nearly forgotten tool of criminal prosecution is being revived and to what extent the prediction of rare events (keyword 'base rate') can be made with sufficient accuracy. The focus of this work is on the compatibility of post-conviction preventive detention with the Basic Law. The central aspect here is the tension between the finality of judicial decisions on one hand and the retroactive effect of statutory regulations on the other. Finally, the compatibility of post-conviction preventive detention with the European Convention on Human Rights is examined.