The gunman at the Mandalay Bay hotel in Las Vegas who shot into a crowd of thousands did it from a room on the 32nd floor. He may have killed many more if not for a security guard who arrived on the floor within 12 minutes of the onset of the attack. Soon, a small group of Las Vegas police arrived. They organized themselves into an ad-hoc SWAT team and began storming room 135.

Tonight, for the first time you'll hear details of the assault from the officers who carried it out.  

One week ago, just after 10 o'clock at night, 22,000 people became targets at a country music concert. Las Vegas detective Casey Clarkson was among them.

Casey Clarkson: The fire just starts hitting us. And you just hear--  

[Body cam: They are shooting right at us, guys, everyone stay down, stay down.]

Casey Clarkson: I just remember, like, it was, like-- like, white spark, like, powder almost, like, hitting the concrete, hittin' the van. I mean, I'm just watching these rounds hit all, like, right next to us. And I'm like, "How is he so accurate?"

Bill Whitaker: Bullets just raining down on--

Casey Clarkson: --it's just raining down the whole time. And I just remember, I'm like, I'm just looking at my gun. I'm just like, "I got a pistol in my hand and this guy's shooting at me with an automatic rifle."

Bill Whitaker: You got grazed. But you-- you have shrapnel.

Casey Clarkson: Yeah, I got a piece of shrapnel in my neck. And I grabbed it for a second. And it was already just pouring blood, dripping off my hand and I was like, oh, my goodness.

Casey Clarkson: And I wanted to try to do more. But my partner was worried because I was getting light-headed at one point.

Casey Clarkson: And I said, "You know what, I'm just gonna stay. And I'm gonna help as many people as I can." 

Bill Whitaker: Doing this while your neck is bleeding.

Casey Clarkson: Yes, sir.

Las Vegas police released department body cam footage of the chaos on the ground as Stephen Paddock fired from above.

Joshua Bitsko: And-- so I hear-- probably Casey's radio traffic-- of, you know, he-- "We're takin' fire. Don't go down the boulevard."

[Police radio: We're trying to see where the shots are coming from if anyone can advise that they're coming from the Mandalay.]

Joshua Bitsko: I just yell to these guys, "Let's go. There's an active shooter."

Sergeant Joshua Bitsko and Officer Dave Newton of the K9-unit had been training dogs when they heard the call.

Joshua Bitsko: So we jump in our cars and hop on the freeway and we were there probably within five minutes.

Detective Matthew Donaldson was doing paperwork at headquarters. He sped nine miles to the Mandalay Bay.  In the chaos, he had to run the last few blocks. His cowboy boots rubbed his feet raw. 

Matthew Donaldson: I took my boots off. I just threw 'em in the casino. That was slowing me down. I was faster barefoot and I was gonna be more effective barefoot.

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