This paper is about a group model building project at the Ministry of Justice in the Netherlands. The aim of the model is to gain insight into the combined effects of an increase in the case load and investments in different phases of criminal justice administration and contextual developments such as increased complexity of cases. A group of representatives from the police force, public prosecution, courts and sentence execution participated in constructing the model from January to August 2004. In this paper we report on reasons for starting the modeling effort and the process of model construction. We then compare the procedure followed to ‘scripts’ – small parts of modeling process that have been tested out in practice and serve as standard building blocks for a group model building project. Scripts specify a technique, the situations for which it is suited and the expected results, enabling a modeler to choose from the wide variety of available modeling techniques. By describing the process followed in this case and consistently relating it to well-established practices we hope to further clarify the modeling process, by contributing to the existing body of modeling techniques and the dissemination of process insights.