"Los Angeles is one of the most under-policed cities in America. With a mere 26 officers for every 10,000 residents (Chicago, by comparison, has 46), the Los Angeles Police Department (LAPD) needs all the help it can get. That help may be at hand, with a modification of technology used to predict another type of threat that the city is prone to: the aftershocks from earthquakes. Big earthquakes are unpredictable. Once they have happened, however, they are usually followed by further tremors, and the pattern of these is tractable. George Mohler, a mathematician at Santa Clara University, in California, thinks something similar is true of crimes."