Mari society was once plaged by violence and crime. At one point, the Mari outlawed violent thoughts and developed a memory adjustment technique to remove the offending engrams from a criminal's mind. After this, crime started to drop immediatly, and three generations later, during the 2370s, virtually no crime was left in their society and only a few law enforcement officers remained in their Constabulary. Before an incident in 2374 one of them, Chief Examiner Nimira, had never dealt with a murder.
The Mari considered their penal system to be enlightened because while those who commited a crime were arrested, they were not imprisoned, the idea of the idea of shutting people away as punishment being considered puzzling and barbaric. Instead, the violent thoughts were removed by Engramatic purge, a quick but somewhat dangerous method, after which the individual was released. Alternatively, extensive Neurogenic restructuring, which might take years, might be employed. Furthermore, as it was considered an irrefutable fact that violent thoughts from others could lead to violent actions, a person telepathically passing on a violent thought to someone who then committed a crime might be charged with aggravated violent thought resulting in grave bodily harm.
However, Mari society had a dark side as well: by the 2270s; a black market had arisen in which many citizens traded in illicit mental imagery. This remained unknown to the Constabulary when a thought harvested from B'Elanna Torres of the Voyager proved so violent that its hosts became unstable. As a result, one Mari individual was badly beaten and another murdered before the culprits were caught.
Even after this underground was uncovered, there was some question if these facts could be believed, and as Voyager left the planet its captain remarked in her log that it was anyone's guess if the justice system would be reformed.
Tuvok remarked that Mari history was similar to that of Vulcans in that both had dealt with crime as a result of exposure to violent thought, by learning to control their emotions. (VOY: "Random Thoughts")