The External Monitor of Forensic Psychiatric Patients (EMT) aims to increase the knowledge of forensic psychiatric patients and the effectiveness of mandatory forensic treatment. In the EMT, five judicial organizations merged their anonymized digital data on (ex-)patients for research purposes. Data originated from the databases of the NIFP, DJI, AVT, 3RO and WODC. By merging this data, a larger part of the trajectory of a forensic psychiatric patient becomes known. Results show that it is possible to combine data from the digital databases of separate organizations for research and analysis purposes. To illustrate the opportunities of the use of merged data, an explorative study was conducted into a current subject. In this study, 218 ‘tbs-patients’ were included and several characteristics of patients of whom the mandatory forensic treatment has ended were compared with those of patients still under mandatory treatment. Suggestions are made for merging data files and for future research.