The Crime and Law Mod adds a new game-play element to Civilization 4. Crime is measured as "Local Instability", and When enough Local Instability occurs, a specific Crime exists in a city. Criminal Buildings increase Local Instability and Decrease Espionage, while Law Buildings, Posts, and Punishments Decrease Local Instability and Increase Espionage.
How Crime is Activated
The potential for Crime is enabled when you research specific Techs like Chiefdom. For example when you research Chiefdom, the ability for Crime (Gangs) to occur is enabled, but exists in the city when its Local Instability Threshold is breached. For example Crime (Arson) has Local Instability Threshold of +250.
Population also generates Local Instability in a city, the higher the Population the more Local Instability it generates.
Criminal Buildings
Crime Buildings = -Espionage + Gold + Local Instability +Anger +Unhealthiness+ Special Benefits
Crime is spread around a city when you create Criminal Buildings in a city like Assassin's Den and Drug Lord's Mansion. This Criminal Buildings provide +Local Instabilty Per Turn. They provide beneficial bonuses and enable special units like Thief and Rogue. Criminal buildings can easily give away all your secrets which reduces in a negative to Espionage, but make up for it by the increase gold from its illegal operations.
Remember that Dog Units can see thieves. However you have to wait until the late prehistoric era to get them. Thus you could potentially spot thieves without ever building a thief yourself.
Law Buildings
Law Enforcement = + Espionage -Gold - Local Instability
Law Buildings decrease Local Instablity Per Turn in each city,and increase Espionage but cost Gold for enforcement. Some Law Buildings provide special bonus like Chief's Hut which provides bonus Experience for Recon Units and others like the Courthouse reduce Maintenance Costs.
Posts
Posts like Town Patrol and Sentry Post provide special bonuses against Rival Spies, and a small handful of City Defense .
Punishment
Punishments like Crucification Crosses and Guillotine provide a Local Stability Bonus per Turn per City.