Purpose of this research is the analysis of the possible connections between the final decision and the judicial truth descending from it. The paper draws a picture on the notion of judicial truth, meant as a result of the evaluation of the themes of the prosecution through the validation of evidence introduced by the parties. Legal certainty and reliability of the final judgment on the merits, no longer subject to further revision, are examined in order to define normative and axiological foundation of the truth arising from the res judicata. In this perspective, the strict respect of the procedural safeguards set forth by the law is not always a sufficient condition for a fair decision, since it does not necessarily aim at the search for truth that the due process model requires.