Recently, terrorist risks are continuing to increase in the form of terrorist acts due to various and simultaneous factors. This subject is of great scientific interest and importance because our society is vulnerable and we have a low level of protection against terrorism. This paper aims at developing a decision support model, called jCatt (jCOLIBRI against terrorist attacks). The preventive model is based on acquiring and reusing past attacks historically solved to assist a decision maker. It helps to understand each terrorist attack situation and to propose possible solutions in the form of preventive and / or corrective measures. It is composed of two main parts: knowledge models described by an ontology, and a reasoning process based on Case-Based Reasoning (CBR). In this paper, we present the development environment used, the architecture and in particular the various components of our model as well as the phases of the reasoning cycle.