In the States, an algorithm is used to predict where and when crimes are likely to take place, so that preventive measures can be taken so they do not occur!
It is based on the system used to predict earthquake repeats.
It does not pretend to be able to catch offenders just before the act.
It just claims that it allowed to prevent certain crimes from being committed, by using prevention where it is the most likely needed. And it boast an impressive reduction in some crime rates in the areas where it has been applied.
More here: http://www.technologyreview.com/news/428354/la-cops-embrace-crime etc ...
Vendor's claims: http://www.predpol.com/results/
Could it be used as a gaydar?