Thanks to the confined (and somewhat crowded) nature of the Enclave, nearly everyone places a high priority on getting along with everyone else. This, as well as the efficiency of the Enclave Watch, keeps crime low.
Nonetheless, occasional property crimes and violent crimes do occur, and a black market in weaponry, magical items, and stolen goods is rumored to exist. Ben's Wares and the Grog Flagon are thought by some to be access points to the black market, as well as a few other places belowground. If it does exist, it operates on a tight web of trust, as nobody seems to know anything specific about it.
There is a wide variety of rumors concerning a Thieves' Guild, which may or may not: be another name for the black market; engage in assassination; have secret contacts with orcish tribes; operate with the approval of the Enclave Watch or certain Enclave Council members; etc. Many think that the Thieves' Guild is pure myth, merely being good grist for tall tales or anecdotes.
Murders or manslaughters are highly newsworthy, due to their rarity. Most assaults happen in the course of drunken fights.
Punishments include monetary or material fines/penalties, imprisonment in the basement of the Enclave Watchtower, or public shaming on Pillory Hill. The death penalty is exercised extremely rarely (once per century or so). Expulsion from the Enclave is never a punishment, in order to keep the location of the Enclave secret from the outside world.
TODO: Justice system? due process? court proceedings?