Predicting Crime Using Twitter and Kernel Density Estimation [pdf]
ptl.sys.virginia.edu
ptl.sys.virginia.edu
(Now that I think about it more, there's also a lot of potential advantages to Twitter: global coverage, uniform data access, less risk of 'juking the numbers', less criteria drift over time... Yes, maybe local police records are much better, but you could spend a lifetime trying to get copies of them and putting them into the same data format and reconciling differing definitions etc.)