In this paper, we disclose the TVR algorithm of the Spanish Criminal Justice System (CJS). This Risk Assessment Instrument (RAI) is mainly applied as part of the decision-making process for granting prison leaves in one of the three prison systems of Spain. This algorithm has been in-use for thirty years but has remained partially undisclosed. After a comprehensive scrutiny of the literature, the original source, in which the algorithm is detailed, was found within an unpublished book. Using the information contained within this manual, we simulated all the possible outcomes of the algorithm. As a result, the algorithm leads to a category of high, very high, extreme, or maximal risk in 99.3 % of cases. Furthermore, out of the 6144 possible outcomes of the TVR algorithm, only 9 outcomes lead to a category of low or very low risk, what entails that there is potential evidence of bias towards false positives.