Crime events require a minimum Crime Rate in a city before it will trigger. Certain buildings raise the Crime Rate, certain buildings lower the Crime Rate. So you are less likely to get a theft in a city with a lot of law buildings than you are in a city with a Gambling House, Market, Smugglers' Port, etc. There is global Crime Rate which is applied to the entire world, and each city has a random initial Crime Rate when it is built (which can be modified by buildings). The global Crime Rate is affected by some Undercouncil resolutions.