The importance of understanding the reasons of past decisions is not a new subject. However, there seems to be a gap regarding the verification of the efficiency of tools for understanding past decisions. In this paper we posit that the ability to perform decision reconstruction, using a GSS solution, can provide a flexible solution to the problem, but only if the information model underneath it is able to support/structure both ways the phases of a decision-making process. Based on earlier work, we present a first proposal for a general information model to support the decision-making process, as well as the decision reconstruction process. We tested these ideas by setting a case study where we used a prototype, based on a proposed model, to analyze a simulated public contracting process and present a discussion based on the obtained results.