Before a lone gunman opened fire in Las Vegas, the city's police department had studied the mass shootings that had rocked the United States in decades prior and learnt a valuable lesson. That lesson may have stopped the massacre from turning out much worse.

Speaking to reporters today Las Vegas sheriff Joseph Lombardo revealed that his officers had learnt from the police responses to the massacres at the Pulse gay nightclub in Florida, Columbine High School in Colorado and the Boston Marathon bombing, among others.

At the time of the Columbine mass shooting in 1999, police were generally taught that the best way to respond to an ongoing incident was to contain the scene and prevent violence from spreading.

Orlando police were criticised last year for responding too slowly when a 29-year-old opened fire at the Pulse nightclub, killing 49 and injuring 53 more. More than three hours elapsed between the initial report of gunfire and when police rammed into the building with a vehicle, finding scores more wounded.

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The same criticism was levelled at New South Wales Police in 2014 when they waited 16 hours to storm the Lindt Cafe during the Sydney siege, after Tori Johnson had been executed.

For police, it's a excruciating decision: Rush in and risk the lives of the officers and captives, or engage with the shooter in the hope of saving lives.

Research from past mass casualty shootings suggest that one person is killed every 15 seconds, so police hesitation can make atrocities worse.

Matthew Helms, who worked as a medic the night of the shooting, visits a makeshift memorial for the victims of the mass shooting. Photo / AP
Matthew Helms, who worked as a medic the night of the shooting, visits a makeshift memorial for the victims of the mass shooting. Photo / AP

Lombardo said his officers were taught that police intervention - no matter how small - had the power to save lives in situations such as the one they were faced with when Stephen Paddock rained gunfire down on a music festival crowd, killing 58 and injuring more that 500.

"I will not disparage another police department's response, but I will tell you we quite often learn from what other people do," he said.

"As a result of what occurred in Columbine, what occurred in Sacramento, what occurred in Boston, what occurred at the Pulse nightclub, police response is changing.

"We have found it's better, instead of securing the perimeter and hoping the person doesn't continue to do acts of carnage associated with their actions, that even a small police response will stop the suspect's actions."

And that is how Las Vegas police acted.

Las Vegas police and emergency vehicles at the scene following the deadly shooting. Photo / AP
Las Vegas police and emergency vehicles at the scene following the deadly shooting. Photo / AP

It took officers 72 minutes from the first 911 call to find the shooter. The response time was lengthened, the sheriff said, because there was so much confusion about where the gunfire was coming from.

Instead of waiting for the SWAT team to arrive at the scene, a small group of officers teamed up with the Mandalay Bay security guards to perform a sweep of the 29th, 30th, 31st and 32nd floors in a desperate attempt to find the exact location of the shooter.

"Officers, on their own, without direction of a supervisor, knew what they had to do," Lombardo said.

"They came together, formed a team, made a response and they didn't wait on SWAT, they said 'We have to stop [him]'.

A woman sits on a kerb at the scene of the shooting outside of the music festival along the Las Vegas Strip. Photo / AP
A woman sits on a kerb at the scene of the shooting outside of the music festival along the Las Vegas Strip. Photo / AP

"It's easy to say 'We'll wait on SWAT, they're the experts in tactical intrusion', but our officers took it upon themselves to act."

In fact, it was a security guard who was first to identify the shooter's location.

The guard was shot at and hit by Paddock as he approached his room as part of the sweep.

People running from the Route 91 Harvest country music festival. Photo / AP
People running from the Route 91 Harvest country music festival. Photo / AP

By the time they had found Paddock's room on the 32nd floor, the SWAT team had arrived and stormed in. Paddock then took his own life.

Lombardo said he was proud of the police response and believed it helped to shut Paddock down earlier than might have otherwise been the case.

"I want to say kudos to those officers that got together, said 'this is what we trained for, active shooter, we'll put an element together, let's go engage this individual and locate them'. And that's what we did," he said.