A mediator was the Edo equivalent to law enforcement officer on Rubicun III.
By the 2360s, the Edo had little need for police, requiring only a very few mediators, who were needed only at one location each day. These locations, known as punishment zones, were known only to the mediators, and were in place for a pre-specified period of time. If a crime was committed, regardless of intent or malice, the mediators arrived on the scene to observe the one responsible for the transgression. Pending admission of guilt or witnesses to the crime, the mediators would enforce the law and almost immediately administer the perpetrator's punishment – invariably execution – carried out by a lethal injection of a fast and painless poison. (TNG: "Justice")