In remarks to the nation's police chiefs in Philadelphia on Monday, Holder said the United States saw an average of five active shooting incidents a year between 2000 and 2008.
"Alarmingly, since 2009, this annual average has tripled. We've seen at least 12 active shooter situations so far in 2013."
The Department of Homeland Security defines an active shooter as an individual actively engaging in killing or attempting to kill in a confined and populated area. Recent examples include the Sandy Hook Elementary School shooting in Newtown, Conn., in December and the Navy Yard shooting in Washington, D.C., last month.
Over the past four years, Holder said, the number of people shot and killed in these incidents is up nearly 150 percent.
"It's become clear that new strategies and aggressive national response protocols must be employed to stop shooters in their tracks," Holder said.
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