Purpose The purpose of this paper is to demonstrate the significance and necessity of adequate management tools to face dynamic complexity. In particular, the paper shows the importance of model‐based support for designing public systems defined through laws. This is illustrated by means of an example: the new reform of the Colombian criminal justice system. Design/methodology/approach Literature review of model‐based reasoning and justice systems. Illustration with a case study: reform of the Colombian criminal process. Findings Human reasoning can be characterized as a model‐based activity, which in turn can be improved by constructing and using diverse models. The support of dynamic models for designing law‐defined public systems represents an open field of research. Specific relevance and conceptualization for criminal justice systems are developed. Originality/value To introduce the significance of the contribution of computer simulation modeling for supporting system design and lawmaking processes.