> In France, my limited understanding, is that the police do not generally investigate but the investigation comes under a judge. They will use the police to gather evidence and interview people but the pressure for a result is on the judge and not the police. The judge should ensure that laws are followed because they are part of the judiciary.

Police investigations in common law countries have judicial oversight, but it seems like a feature rather than a bug to separate judges from investigators. If the judge is in charge of the investigation, who's going to stop the judge from issuing unreasonable search warrants?