Agree with GreenKnight. Surveys in the US have strongly suggested that the bulk of the reduction in crime during the nineties was down to a combination of improved law enforcement, as pioneered by Bratten in NY - and lately LA - and rampant job creation. The increased risk of detection and several years in the soap-on-a-rope club made even menial work more lucrative in all senses to the non-hardened crim. If you have access to The Economist's online edit the reports will be archived in there.