Today Facebook, Twitter, Google as well as the specific police technologies like PredPol or ShoySpotter help the police to more effectively identify crimes and, what is more important, to predict them before they happen. There is one basic principle behind crime prediction algorithms: future crime will appear in accordance with probability distribution received from huge historical databases. There are numerous disputes on ethics, privacy, and validity of outcome along with the evolution of new policing method, but the results are quite positive: so, homicide rate in the US (the United States is the leading country in applying new method) reduced by 6 percent in average from 2000 to 2011. Concerning burglary, it also decreased through the period at a glance, except housebreaking. Of course, there are a lot of other factors behind these changes, but new policing technologies seem to be a rather significant factor.
Based on article "How Facebook could get you arrested": http://www.guardian.co.uk/technology/2013/mar/09/facebook-arrested-evgeny-morozov-extract