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‘Predictive policing’ harnesses computers to head off crime

LOS ANGELES — Los Angeles police are aiming to beat suspects to the scene of a crime by using computers to predict where trouble might occur.

The city’s police department is the largest agency to embrace an experiment known as predictive policing, which crunches data to determine where to send officers to thwart would-be thieves and burglars. Time Magazine called it one of the best inventions of 2011.

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Early successes could serve as a model for other cash-strapped law enforcement agencies, but some legal observers are concerned it could lead to unlawful stops and searches that violate Fourth Amendment protections.

In the San Fernando Valley, where the program was launched last year, officers are seeing double-digit drops in burglaries and other property crimes. The program has turned enough in-house skeptics into believers that there are plans to roll it out citywide by next summer.

‘‘We have prevented hundreds and hundreds of people coming home and seeing their homes robbed,’’ said police Captain Sean Malinowski.

Crime mapping has long been used to determine where the bad guys lurk. The idea has evolved from colored pins placed on a map to identifying ‘‘hot spots’’ via a computer database based on past crimes and possible patterns.

Over the past decade, many large police departments, including in Los Angeles and New York City, have used CompStat, a system that tracks crime figures and enables police to send extra officers to trouble spots.

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The new program used by the Los Angeles Police Department LAPD and police in Santa Cruz, Calif., is more timely and precise, proponents said. Built on the same model for predicting aftershocks following an earthquake, the software promises to show officers what might be coming based on simple, constantly calibrated data: location, time, and type of crime. The software generates prediction boxes — as small as 500 square feet — on a patrol map. When officers have spare time, they are told to ‘‘go in the box.’’

The goal is not to boost the number of arrests. Officers want to intercept a crime in progress or deter would-be criminals. ‘‘I want to disrupt an activity before an arrest is made,’’ Malinowski said. ‘‘You can’t arrest your way out of some of these problems.’’

Jeff Brantingham, an anthropology professor at the University of California Los Angeles, said the data are also derived from criminal behaviors — repeat victimization and the notion that criminals tend not to stray far from areas they know best.

‘‘If you are victimized today the risk that you’ll be a victim again goes way up,’’ said Brantingham, who cofounded a software company tapped by the LAPD for its program.

So far, the program has been implemented in five divisions that cover 130 square miles and roughly 1.3 million people. In the valley’s Foothill Division, where more than half of the crimes committed are property-related, about 170 patrol officers are spending 70 hours a week working in the boxes.

In one instance, a police captain questioned sending officers into a box that was on the edge of his coverage area. Officers went out and didn’t find anything, but returned several nights later and found someone breaking a window.

The division leads the department in crime reduction, Malinowski said. Crimes were down in the area 13 percent following the rollout, compared to a slight uptick across the rest of the city.

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