Mapping Crime: Principle and Practice
This publication (PDF) from the National Institute of Justice offers an introduction to mapping crime and GIS.

Sourcebook of Criminal Justice Statistics
A fascinating statistical look at crime in the U.S.; many charts include state-by-state breakdowns.

Statistics
From the About.com Crime site, a plethora of links to crime-related statistics.

Uniform Crime Reports
The FBI's annual report of serious crime in cities across the U.S.

Why Map Crime?
An excellent overview (with example maps) of why mapping crime is useful.