Another mass shooting in America, this time at the Church of Jesus Christ of Latter-day Saints in Grand Blanc, Michigan.

Law enforcement there is being praised for its rapid response that may have saved lives.

Responding to a mass shooting is a reality for law enforcement agencies. There have been more than 320 this year, according to the gun violence archive. And in each case, seconds can mean the difference between life and death.

Gene Petrino is a retired SWAT commander. He says law enforcement response protocol changed after the 1999 Columbine High School shooting.

"Back then, it was believed that we would wait until tactical teams could be in place," Petrino said. "We've gone to a new method where essentially the first officer on scene is going in."

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