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Attorney General Eric Holder's most urgent point in an address to a conference of police chiefs in Philadelphia on Monday: Mass shootings are on the increase, and police need to be prepared. Research shows that only about half of all such incidents from 2000 to 2010 involved police — and law enforcement only resolved one-third of all of the attacks. Even as Holder spoke, a shooting was unfolding at a middle school in Nevada.

Holder's speech noted the increase in mass shootings in recent years.

"Between 2000 and 2008, the United States experienced an average of approximately five active shooter incidents every year. Alarmingly, since 2009, this annual average has tripled. We’ve seen at least 12 active shooter situations so far in 2013. Even more troubling, these incidents seem to be getting more and more deadly.

Over the last four years, America has witnessed an increase of nearly 150 percent in the number of people shot and killed in connection with active shooter incidents."

The increase can be seen at right. (Data for 2011 and 2012 wasn't immediately available.) If you're curious, the FBI's definition of an active shooter event is "an individual actively engaged in killing or attempting to kill people in a confined and populated area." An on-going shooting, if you will — one in which law enforcement could intervene.

This is a starkly different definition than the one behind our recent analysis of future events. That definition is based on the number of people killed. But the resulting picture of the incidents is similar. A December 2012 report from the FBI and DHS suggests that shooters were overwhelmingly male and the majority of incidents occurred at places of business.

Holder's point, though, was less about the number of shootings and more about the appropriate response. At its "Active Shooter and Mass Casualty Incidents" page, the FBI links to a study conducted by researchers at Texas State University. That study looked at the 84 active shooter events from 2000 to 2010, and mapped out how each was resolved — with or without police, with or without the shooter being captured alive.

We've taken the flowchart created by the researchers and simplified it somewhat. Each of the 84 incidents ends in one of the outcomes in the bottom row.

In only about half of the incidents was the shooting resolved after police arrived. Only about 8 percent of the time did the incident end with a suspect being subdued by law enforcement.

Here's another way to look at it. Forty percent of the time, the shooter committed suicide. Thirteen of the 84 times, victims of the shooting were able to subdue the shooter — almost twice as often as law enforcement was able to do so.

That's because the standing orders in such events has generally been for first responders to wait until specialized officers arrive. Holder encouraged the police to change their standard response to intervene more quickly.

"The reality is that police don’t always have the luxury of time to get their most highly-trained, best-equipped officers on the scene. To save lives, the first officers to arrive must sometimes be the ones to directly engage an active shooter. That’s why all law enforcement officers must have the best equipment and most up-to-date training to confront these situations."

The Texas State researchers considered what happened when an officer acted to intervene before waiting for back-up. In eight of 14 incidents — 57 percent of the time — the officer played a role in concluding the incident, including one capture and five incidents in which the perpetrator was shot. But then there's another data point: on two occasions of those latter six, the officer was also shot. That's one-third of the time — in a rather small sample.

It could be worse, according to Holder. The FBI's Behavioral Threat Assessment Center, he said, "has reported hundreds of successful disruptions" of potential shooters — "including an anticipated 150 this year alone." The details of those disruptions were not conveyed.

By the way, the FBI has a pamphlet on how best to respond in the event of a shooter incident. "Act with as much physical aggression as possible" if you have to fight, and "improvise weapons or throw items" at the perpetrator. "Commit to your actions," it reads. "Your life depends on it." And if historical data is any guide, you've got nearly as good a chance at resolving the event as the police.

This article is from the archive of our partner The Wire.