The preliminary investigation in Mexican law is a legal institution consisting of a series of preliminary rulings necessary for the Public Prosecutor (Prosecutor) to determine if it is appropriate to bring criminal proceedings before the courts. It has also been called: administrative instruction, preparation of the action, preprocessing, preparatory phase, among others.
It begins with an opening resolution known as auto ad inquirendum or self-defense and ends with the exercise of criminal action (promotion of the action), when the prosecutor's opinion there are sufficient elements that make presume the probable responsibility of the indicted in the commission of an offense, issuing an order of filing (administrative acquittal), which occurs when, in the opinion of the public prosecutor, there are no constitutive elements of crime, or reserve (administrative suspension), when there are means that make presume the probable commission of a crime but they are not enough to bring criminal action.
Other objects of the preliminary investigation are: giving assistance to the victims of crimes, applying precautionary measures, carrying out investigations, supplying preparatory means, issuing burial orders for corpses, documenting their activities, among others.
In this procedure, the public prosecutor assumes a quasi-jurisdictional position, given that the latter, when conducting non-legal investigative activities, judges whether the conduct that has been notified as criminal (notitita criminis) is or is not; although in reality what determines is whether there are elements that indicate the existence of a crime and the probable responsibility of a subject (active in the material relationship).
Article 21 of the Constitution empowers the Public Prosecutor's Office to prosecute crimes, being aided in its functions by the federal ministerial police. When the preliminary investigation stage begins with the prosecutor having a person or persons detained, it has a fatal term of 48 hours, which can be doubled at the request of the alleged perpetrator or in cases of organized crime, to resolve the legal situation of these .
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