The existence of law enforcement agencies in the Republic is considered not as protectors and protectors, but often backfires and social problems because what is aspired are not by the reality. Nevertheless, the community continues to voice the law as what is desired even though sometimes it is ignored but still struggling. The law desired by society is necessarily a law that lives sociologically. At the level of investigation in the police, even if someone is suspected of having committed a minor criminal offense, the police will still apply the concept of the investigation by the prescribed criminal procedure law. In the current system of investigating criminal cases, the government continues to seek reasoning mediation against the background of thoughts that are associated with the ideas of renewal of criminal law (penal reform) and associated with the problem of pragmatism. The background of the ideas of "reforming reasoning" includes the idea of victim protection, technical ideas, the idea of restorative justice, the idea of overcoming rigidity/formality in the prevailing system, the idea of avoiding the adverse effects of the criminal justice system and the current criminal system, in particular in seeking other alternatives to imprisonment (alternative to imprisonment/alternative to custody). The problem that can be raised from this paper is how the position of a system of reasoning mediation in the police investigation system on objects and how the opportunities and prospects for the implementation of a penal mediation system as an effort to discuss criminal law in Indonesia. This research study is normative juridical research by looking at national criminal law as a rule or norm in the enforcement of criminal law. The researcher will see the principle of legality in national criminal provisions both in principle and in the application of law enforcement. In normative juridical research, the type of data used is secondary data obtained from library data.