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ARVADA, Colo. (KDVR) — The law enforcement officers who responded to reports of an active shooter in Olde Town Arvada Monday did exactly what they were taught, according to a retired sergeant who spent decades training officers nationwide.

“It’s a mass shooter situation. You have to be quick. You have to be decisive. And they were,” Grant Whitus, a retired Jefferson County Sheriff sergeant said.

Whitus began one of the first active shooter training programs in the country after he was one of several officers that responded to the Columbine shooting.

“They’ll go right to where the gunfire is, obtaining information from witnesses (about) where the person might be,” Whitus said.

Arvada Police have not released many details of the shooting that killed three people in the downtown business district Monday afternoon. Sources have said that a gunman with a hatred for law enforcement ambushed Officer Gordon Beesley, who died. Witnesses said Johnny Hurley, described as a ‘Good Samaritan’ by police then shot the gunman. Law enforcement sources told FOX31 that a responding officer shot Hurley. An exact timeline of events is unclear.

“They certainly don’t have time to engage in a conversation about dropping the gun,” Whitus said about officers responding to an active shooter call. “So, they take the shot immediately. I certainly would’ve done the exact same thing. Any reasonable officer that’s trained would’ve done the exact same thing.

“Unfortunately, it was tragic,” Whitus added.

Whitus commended what Hurley did and called him a hero.

“My heart is with the Hurley family. And Officer Beesley (and) his family,” Whitus said. “We also have to keep in our thoughts, that these are great officers doing exactly what they were trained to do. And they were stopping what they thought to be the mass shooter. Unfortunately, it was tragic.”