To gain insight into the success and possible bottlenecks in the criminal justice domain, good and trustworthy management information is required. This paper presents a case study of a data space system that facilitates the monitoring of data flows within as well as between organizations involved in the Dutch criminal justice system. To build such a system several challenges are faced. Data from heterogeneous sources are extracted and related by means of domain knowledge. A proper system architecture is developed based on the concept of data spaces. Our data space system consists of three layers: a data space, a space manager, and an interface layer. The data space layer consists of a set of heterogeneous databases. The space manager layer – implemented as a variable database and a relationship module – consists of domain knowledge. The relationship module decides which databases in the data space layer are required to answer a query. The interface layer consists of a user friendly web interface, which facilitates policy makers to interpret data flows within the justice domain. The evaluation of our system shows that it has an added value in improving policy monitoring and accountability by clarifying goals and providing insightful indicators.