More details released about critical 12 minutes of Las Vegas mass shooting

(ABC News) — New details have emerged about those 12 critical minutes as police responded to the Las Vegas massacre.

ABC News has learned that there were police officers in the Mandalay Bay hotel, securing another event when Stephen Paddock opened fire. But the hotel complex is so vast that police say officers who were across the street at the country music concert got there faster running through the streets in that rain of bullets.

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By the time police arrived, the shooting had stopped, twelve minutes after security officer Jesus Campos was wounded and called on radio for help.

In his first interview, Campos told Ellen DeGeneres that he’d been sent to investigate an open door in the stairwell.

“As that door is closing, and it’s so heavy, it’ll slam, I’m walking down this way and I believe that’s what caught the shooter’s attention,” Campos said. “As I was walking down, I heard rapid fire.”

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With this new timeline, the remaining mystery is why did the shooter do this? Police say that he was so secretive, that we may never know.