WASHINGTON — Attorney General Eric Holder said Monday the average number of mass-shooting incidents has tripled in recent years.

Between 2000 and 2008, the U.S. experienced an average of five mass shootings every year. Since then the annual average has tripled, Holder said. So far in 2013, there have been at least 12, he said.

According to Justice Department figures on mass shootings, 404 people were shot and 207 people were killed from 2009 to 2012. From 2000 to 2008, 324 people were shot and 145 were killed.

In remarks to the annual conference of the International Association of Chiefs of Police, the attorney general said that in the past decade, the Justice Department has helped train 50,000 front-line officers, more than 7,000 on-scene commanders and more than 3,000 local, state and federal agency heads on how to respond to active shooters.

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To disrupt planned shootings and other attacks, the FBI’s Behavioral Threat Assessment Center works with local police and other levels of law enforcement to assess people who may be contemplating violence. Since 2011, the center has reported hundreds of successful disruptions, including an anticipated 150 this year alone, Holder said.

Giving police officers the tools to respond to mass shootings was the top concern for Holder in his address to more than 1,000 state and local officers.

“We’ve seen in the last year, it’s almost always patrol officers who are responding to active shooters, not SWAT teams,” said Holder, referring to the mass shootings in Newtown, Conn.; Aurora, Colo.; and the Washington Navy Yard.

The Department of Justice is developing guides for schools and churches to respond to active shooters and is providing training for local officers on how to respond to such incidents.

Holder also discussed the Justice Department’s new push for drug treatment for some federal drug crimes instead of mandatory minimum sentences. Saving money on incarceration will leave resources to pursue bigger cases against more serious criminals, he said.

The Justice Department’s response to new state marijuana-legalization laws, however, was loudly opposed.

“We strongly disagree with the recent decision not to challenge the marijuana laws in Washington and Colorado,” said Craig Steckler, association president and retired chief of the Fremont, Calif., Police Department, to applause.

The Justice Department announced in August that it would allow state marijuana legalization to go forward and advised U.S. attorneys to prosecute marijuana users or businesses only if they were involved in trafficking or giving marijuana to minors.

“We are disappointed with the decision,” Steckler said. “We think we’ve opened the floodgates to people who want to fully legalize all drugs.”

Holder and new FBI Director James Comey, who also spoke to the officers, warned that sequestration — the automatic across-the-board federal budget cuts — will hurt local police agencies.

“I don’t think folks understand the coming impact of sequestration on the FBI and our partnerships with state and local law enforcement,” said Comey, who noted that those partnerships were essential during the Navy Yard shooting Sept. 16, his first day in his new position.

The organization also honored Newtown Police Chief Michal Kehoe during the meeting.