This is a reflective job of approaching to the procedure of the Preliminary Investigation, as an action that aims to establish principles of truth about the facts that are brought to the attention of the authority; and that it is a response to the obligation to seek the truth regarding God and his Church. Based on the indication of c. 1717, the IP is defined as a means of conviction that proves the occurrence of the crime, in this case of sexual abuse of a minor or vulnerable person, by establishing moral certainty the authority has elements to decide on the initiation of a proper criminal proceeding saying. The historical and canonical analysis of the IP follows the timeline of the guiding and normative documents of the Church developed to respond to complaints of sexual abuse whose alleged actor is a cleric. These indications and norms were compiled and systematized in 2020, in the Vademecum on some procedural issues in cases of sexual abuse of minors committed by clerics, which is a guide under permanent construction so that the actions of the competent authority are effective and adjusted. to canon and civil law.