Op-Ed: First came data-driven policing. Now comes data-driven prosecutions.

Prosecutors’ offices are finally joining the intelligence revolution that has transformed policing since the 1990s. That revolution dates to 1994, when William J. Bratton took over the New York Police Department and declared that his goal was to prevent crime, not just respond to it. Bratton’s new proactive mission for the NYPD required the department to closely analyze crime data on a daily basis and to refine its tactics and deployment according to what the data showed. Bratton’s paradigm shift, known as Compstat, quickly spread through police departments across the country.

Prosecution, however, has remained in a reactive mode. District attorneys generally view their role as doing justice in the individual cases that the police bring to them; they are less likely to consider the effect a prosecution might have on broader lawlessness or how a defendant fits into the criminal landscape. Vital information about offender networks gleaned in the course of preparing a case for trial remains on a prosecutor’s legal pad without getting conveyed back to the police or to other prosecutors. With few exceptions, prosecutors have gauged their success by convictions, not by crime declines.

That reactive mind-set is changing, however, aided by the exploitation of social media and other cutting-edge technologies. Prosecutors from San Francisco to New York are reconceptualizing their mission to include preventing violence, and they are developing information-sharing systems to accomplish that goal.

The Manhattan district attorney, for example, created a Crime Strategies Unit in 2010 with the single goal of gathering and deploying intelligence on Manhattan’s crime patterns and its most serious offenders. The unit has compiled a database of Manhattan’s most significant criminal players — now numbering about 9,000 — whose arrest anywhere in the city immediately triggers an alert to one of the Crime Strategies Unit attorneys. The attorney will then contact the local prosecutor who has been assigned the case — whether in Manhattan or another borough — to make sure the defendant is prosecuted to the full extent of the law rather than slipping through the cracks.

The arrest alert system recognizes that a defendant’s official history of arrests and convictions may fail to convey his position in the criminal food chain. A 16-year-old gang member may be responsible for numerous shootings, as attested to by his and others’ Facebook pages, but never arrested for any of them because his victims and witnesses refused to cooperate with the police.

If he is nabbed for shoplifting, the misdemeanor prosecutor will have a few minutes at most to decide whether to pursue the case. Seeing simply a petty vandal, the charging attorney might well let him walk free. But if that attorney is armed with intelligence gathered on the suspect, he can seek the maximum charge and argue to the judge for high bail. And if detectives have asked to be included in the arrest alert system, they can pay the suspect a visit in jail and see whether he is prepared to cooperate with them.

The arrest alert system also recognizes that a small number of individuals commit a disproportionate amount of crime. “It’s not so much that there are crime hot spots as hot people,” says Lauren Baraldi, a prosecutor in the Philadelphia district attorney’s office, which is replicating Manhattan’s Crime Strategies Unit. Incapacitate those crime drivers and you will produce an outsize effect on public safety.

Social media are central to intelligence-driven prosecution. The value of social media to law enforcement became clear after New York police officers arrived at the home of a Brooklyn gang member who had just been shot, and watched the tweets from his fellow gang members planning revenge pop up on his open cellphone as the gangbanger lay dying in front of them.

Intelligence-driven district attorneys constantly track the Internet footprints of suspects in their arrest alert database. The Facebook postings and Twitter feeds of gang members bragging about retaliatory shootings have provided the backbone for several recent gang conspiracy cases in Manhattan. Facebook messages among now-convicted East Harlem gang members, for example, included admonitions to close in on rival gang members before shooting them and to not hog communal guns.

Prosecutors in Richmond, Va., and Rockland County, N.Y., as well as San Francisco and Philadelphia, are building intelligence systems to drive crime down. And the rethinking of prosecution has only begun. San Francisco Dist. Atty. George Gascon is exploring the idea of predictive prosecution, echoing the nascent predictive policing concept.

“We want to create tools to project crime patterns several years out” by mapping the connections between victims and offenders in a neighborhood, Gascon says. And he wants better ways to measure whether his office’s court filings are targeted efficiently.

Violent crime has dropped by more than 40% nationally since 1993, thanks to the spread of Compstat policing. Keeping that crime decline going will require every component of the criminal justice system to be at the top of its game. Intelligence-driven prosecution is coming not a moment too soon.

Heather Mac Donald is a fellow at the Manhattan Institute and a contributing editor to City Journal. This article is adapted from its summer issue.

Follow the Opinion section on Twitter @latimesopinion