Possessing magic is not illegal, but using it without permission is. The type of magic used, or how vulgar it appears to be, strongly determines how harsh the penalty will be. Casting a small light or creating a dancing flame is usually overlooked or treated with a slap on the wrist. Most citizens don't bother to report that kind of activity unless it becomes pervasive. Stronger magic, used for example to lift a heavy object or summon something into existence, is met with imprisonment in Justice Hall (sometimes for several years but usually under a year), examination/interrogation, and sometimes torture. It is up to the perpetrator to convince the Judges that she/he will not be a further threat to the city before being released.
Using magic in any way to harm another creature is the gravest offense, and is treated much like murder. Long term imprisonment and torture is almost certain, and execution is likely if the target was another citizen. Of course, anyone who uses magic to evade or injure a guardsman or some other city official is guaranteed to be tortured and executed.
Declaration of Magical Ability
Any newcomers to Marn who have magical abilities are instructed to report directly to Justice Hall and explain the nature of their magical powers. Under normal circumstances a file is created outlining said person's powers for security purposes. If the powers are deemed extremely dangerous, the person may be exiled from the city.
There are rumors that some outsiders who have entered Justice Hall to declare extremely dangerous powers were never seen again. The Judges neither confirm nor deny any rumors regarding such extreme cases, but maintain that any and all actions taken are done to protect the citizens of Marn.
All non magic related crimes are handled by the City Guard and are only forwarded to the Judges if the crime directly threatens the stability and security of the city. Even in cases where major crimes and sabotage are suspected, the City Guard may choose to handle it themselves. The Judges wield more power, and sending a man to the Judges is a last resort. The City Guard have a large degree of freedom to enforce the law and punish criminals as they see fit. Execution for non-magical offenses is rare and usually only applies to murder. The prison cells located inside the Guard Headquarters are unpleasant but not inhumane.
Slavery of humans and elves is illegal in Marn. The only slaves that can be kept legally are creatures that are deemed to be less than sentient, such as goblins, which are often viewed more as pets than slaves.
Personal disputes and petty crimes not worth the attention of the City Guard are handled by elected civil magistrates.