PHILADELPHIA (CNN) -- Attorney General Eric Holder said Monday that it has become clear new strategies are needed to deal with how police respond to "active shooter" situations -- those in which someone with a gun is still on the scene and firing at victims.

Shootings like last month's at the Washington Navy Yard have tripled in recent years, Holder told the International Association of Chiefs of Police Conference, and there have been 12 already this year. And he said such shootings have become more deadly -- a 150 percent increase in the number of people killed over the past four years.

"Although research methods and results vary, it's become clear that new strategies -- and aggressive national response protocols -- must be employed to stop shooters in their tracks," Holder told the police chiefs.

In the Navy Yard shooting, the police response time was considered extremely fast. D.C. Metro Police Chief Kathy Lanier said her officers were on the scene in seven minutes, which is about half the national average response time.

But still, 12 people were killed.

Experts say that despite a quick response time, the first officers on the scene often must wait until more highly trained special weapons and tactics teams arrive, and in the interim lives could be lost.

Holder said that years of analysis reinforces the need for "an immediate, aggressive response to active shooters. In order to prevent additional casualties, it is often patrol officers -- not necessarily SWAT teams -- who serve as the tip of the spear in responding to these incidents."

Security consultant Chris Grollnek describes current tactics as, "Respond once your backup arrives, and use a contact-cover approach so you are not on a suicide mission."

Holder said that police don't always have the luxury to take the time to get their best-trained, best-equipped officers to the scene.

"To save lives, the first officers to arrive must sometimes be the ones to directly engage an active shooter," Holder said. "That's why all law enforcement officers must have the best equipment and most up-to-date training to confront these situations. We owe these officers nothing less."

Grollnek focuses on training regular people how to protect themselves before police arrive at the scene. He says people who work in places where a shooting could happen could use some training, too.

"Get up and move -- do not become a victim, don't be a stationary target," he said. "React by escaping the target."

Holder said the Justice Department has partnered with groups like the IACP to train more than 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 shooter situations. And it has joined with other federal agencies, local partners and outside experts to develop guidance for schools, churches, colleges, universities and private citizens on how to prepare for such incidents.

Holder also said that the Justice Department has placed an increased emphasis on evaluating threats with the goal of disrupting potential shootings and other violent attacks. The FBI's Behavioral Threat Assessment Center has successfully disrupted hundreds of potential shootings --including 150 this year --Holder said.

While Holder pointed to partnerships with the IACG in active shooter response and prevention, there is disagreement on other issues: IACG President Craig Steckler, retired chief of police in Fremont, Calif., said in his introduction of Holder that the group's membership "profoundly disagrees" with the Justice Department's decision not to challenge laws legalizing marijuana in Colorado and Washington state and not taking a stand against legalizing marijuana in California, as that state's Proposition 19 would do.

"This decision by the U.S. Department of Justice, in our view, will open the floodgates for those who want to legalize marijuana throughout the country, those who have the resources to place initiatives and referendums on state ballots and those who've continued to profit from the sale of this unlawful drug," Steckler said to applause.

Holder said the Department of Justice and law enforcement agencies need "marriage counseling" in dealing with some issues.

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