Although the Conclave establishes civil law much as any planet-based democracy, enforcement and trials are more unique. After the flight from the geth, there were few constables to police the millions of civilians aboard the Fleet, so the navy parceled out marine squads to maintain order and enforce the law. Today, quarian marines have evolved training and tactics akin to civilian police but remain adept at combat in the confine spaces of a starship and fully under the command of the military.
Once taken into custody, the accused is brought before the ship's captain for judgment. While the ship's Council may make recommendations, tradition holds that the captain has absolute authority in matters of discipline.
Most are lenient, assigning additional or more odious maintenance tasks aboard the ship. Persistent recidivists are "accidentially" left on the next habitable world. This practice of abandoning criminals on other people's planets is a point of friction between the quarians and the systems they pass through. Captains rarely another choice; with space and resources at a premium, supporting a non-productive prison population is not an option.
In the early years, many quarian freighters were armed and used as irregular "privateers." Civilian ships still show a strong preference for armament, making them unpopular targets for pirates. Though they have rebuilt their military, there are still mere hundreds of warships to protect tens of thousands of ships. The quarian navy follows strict routines of patrol and takes no chances. If the intent of an approaching ship can't be ascertained, they shoot to kill.