At least 58 people were killed and 515 were injured in Las Vegas on Sunday night when a gunman opened fire on a music festival crowd from the 32nd floor of the Mandalay Bay Resort and Casino. It was the deadliest shooting in modern U.S. history.

The “nonstop gunfire,” according to one witness, sent more than 22,000 country music fans scrambling for their lives. Police say the lone suspect had at least 10 rifles when he was found dead in a Mandalay Bay hotel room.

Terrified bystanders ducked, ran, then sprang into action — frantically caring for the wounded. As ambulances rushed to the scene, concert-goers made makeshift stretchers out of police barricades. They plugged wounds with their bare hands and used their clothing to try to stanch eachother’s bleeding. At least one man described a stranger dying in his arms.

An off-duty Las Vegas police officer who was attending the concert was among the dead, police said.

PHOTO: A man lays on top of a woman as others flee the Route 91 Harvest country music festival grounds after an active shooter was reported on Oct. 1, 2017 in Las Vegas. The woman later was seen getting up with help. (David Becker/Getty Images)
PHOTO: A man lays on top of a woman as others flee the Route 91 Harvest country music festival grounds after an active shooter was reported on Oct. 1, 2017 in Las Vegas. The woman later was seen getting up with help. (David Becker/Getty Images)
PHOTO: People run from the Route 91 Harvest country music festival after gun fire was heard, Oct. 1, 2017 in Las Vegas. (David Becker/Getty Images)
PHOTO: People run from the Route 91 Harvest country music festival after gun fire was heard, Oct. 1, 2017 in Las Vegas. (David Becker/Getty Images)

In the wake of the shooting, the Las Vegas Police Department said authorities responded to a hotel room on the 32nd floor of the Mandalay Bay hotel, where police said the suspected gunman, 64-year-old Stephen Paddock, was dead. Police said they believe Paddock, of Mesquite, Nevada, killed himself prior to police entry.

The motive was unclear. Officials said at a news conference this morning they have found no connection between the shooting and any international terrorist group.

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Videos filmed by onlookers gave a window into the chaos that ensued, with some thinking that fireworks were going off. The bullets rang out over the final night of the Route 91 Harvest Music Festival, which was taking place across the street from Mandalay Bay. Jason Aldean was the night’s headliner; other performers included country stars Jake Owen, Big & Rich, Luke Combs and Dylan Scott.

PHOTO:Las Vegas strip shooting after a gunman opens fire near Mandalay Bay casino, Oct 1, 2017. (ABC News)
PHOTO:Las Vegas strip shooting after a gunman opens fire near Mandalay Bay casino, Oct 1, 2017. (ABC News)

Witness Brian Claypool said on “Good Morning America” today that after the first round of gunfire, he ran into a little room that he described as a production area.

“The hardest for me was, I saw six young women. They were maybe 20, 22. They were all crying on the ground. I was trying to be calm,” Claypool said, appearing emotional.

“But I thought at the moment of the Orlando shooting, because we were in this room,” he said of the 2016 Pulse nightclub shooting that left 49 people dead. We didn’t know where the shooter was. We thought he was going to jump the fence and come in this room and shoot us all. … I’m thinking, ‘Am I going to die in this room?'”

“Then the shooting stopped,” Claypool said, “And I peeked out the front of the door, I peek my head out, police officers scream, ‘Go! Go!’”

Claypool said he tried to bring comfort to the young women who were sheltering in the room with him.

“I said to myself, ‘These girls aren’t going to die. I’m not going to die,” he said. “I need to get home to see my daughter. This is not happening.'”

PHOTO: People scramble for shelter at the Route 91 Harvest country music festival, Oct. 1, 2017, in Las Vegas. (David Becker/Getty Images)
PHOTO: People scramble for shelter at the Route 91 Harvest country music festival, Oct. 1, 2017, in Las Vegas. (David Becker/Getty Images)