In Brazilian legal system - unlike the majority of others Roman-based ones - the same judge is responsible either to allow investigative police diligences and to do court ruling on criminal cases. This responsibility is given by the procedural institute of “prevention”, which in Brazilian law means the obligation of the judge who works previously in a case to finish it until the court ruling. The Author thinks that a change in this system is urging. “Prevention” institute determines that the same judge that works in the non-judicial preliminary investigation must work in the subsequent criminal case. Every decision made by a judge, ordinary human being as all of us, naturally full of opinions and prejudices, is a valor attribution. The judge takes decisions every time in non-judicial preliminary investigations, determining provisory arrests and search warrants, for example. To separate preliminary judge and definitive court is to defend impartiality, as court judges cannot decide based in preliminary material, only in proofs produced by contradictory on the definitive stage. This paper analyses the “Guarantee Police Court”, which is applied in most of Roman-based European legal systems and generates a new discussion in Brazil, as the brand-new Criminal Procedure Act approval by Brazilian Congress is each day closer.