The victims just kept coming.
In cars, in ambulances waiting four or five deep, from the walking wounded to the barely alive, they arrived in droves.
"I have no idea who I operated on," said Dr. Jay Coates, a trauma surgeon whose hospital took in many of the wounded after a gunman opened fire from his 32nd-floor hotel suite Sunday night on a country music concert below. "They were coming in so fast, we were taking care of bodies. We were just trying to keep people from dying."
It was the deadliest mass shooting in modern U.S. history, with at least 58 killed and 527 injured, some by gunfire, some during the chaotic escape. Scores remained in critical condition Tuesday.
Authorities say the gunman set up cameras inside and outside the hotel room where he opened fire on the crowd at a country music concert.
Sheriff Joe Lombardo said at a news conference Tuesday that he believes Stephen Paddock set up the cameras to see if anyone was coming to take him into custody. He did not release further details.
The sheriff also said authorities had completed their investigation at the gunman's property in Reno, finding five handguns, two shotguns and a plethora of ammunition.
University Medical Center of Southern Nevada was one of many hospitals that were overflowing Tuesday.
"Every bed was full," Coates said. "We had people in the hallways, people outside and more people coming in."
He said the huge, horrifying wounds on his operating table told him this shooting was something different.
"It was very clear that the first patient I took back and operated on that this was a high-powered weapon," Coates said. "This wasn't a normal street weapon. This was something that did a lot of damage when it entered the body cavity."
The gunman, 64-year-old high-stakes gambler and retired accountant Stephen Paddock, killed himself as authorities stormed his hotel room at the Mandalay Bay hotel casino.
He had 23 guns — some with scopes — in the room where he had been staying since Thursday. He knocked out two windows to create sniper's perches he used to rain rapid fire down on the crowd of 22,000 people some 500 yards away.
He also had two "bump stocks" that can be used to modify weapons to fire continuously, as if fully automatic, according to two U.S. officials briefed by law enforcement who spoke on condition of anonymity because the investigation is still unfolding.
At Paddock's home, authorities found 19 more guns, explosives and thousands of rounds of ammunition. Also, several pounds of ammonium nitrate, a fertilizer that can be turned into explosives, were in his car, authorities said.
The FBI discounted the possibility of international terrorism, even after the Islamic State claimed responsibility for the attack. But beyond that, the motive remained a mystery, with Sheriff Joseph Lombardo saying: "I can't get into the mind of a psychopath at this point."
While Paddock appeared to have no criminal history, his father was a bank robber who was on the FBI's most-wanted list in the 1960s.
"I can't even make something up," his brother in Florida, Eric Paddock, said when asked what might have motivated his brother. "There's just nothing."
President Donald Trump on Tuesday called the gunman "demented" and a "very, very sick individual." Asked about gun laws, the president said, "We'll be talking about gun laws as time goes on."
His muzzle flashes visible in the dark, Paddock began shooting just after 10 p.m. and appeared to fire unhindered for more than 10 minutes, according to radio traffic, as police frantically tried to locate him.
"We can't worry about the victims," an officer said over the radio at 10:15 p.m. "We need to stop the shooter before we have more victims. Anybody have eyes on him ... stop the shooter."
The crowd, funneled tightly into a wide-open space, had little cover and no easy way to escape. Victims fell to the ground, while others fled in panic. Some hid behind concession stands or crawled under parked cars.
Faces were etched with shock and confusion, and people wept and wailed. Some of the injured were hit by shrapnel. Others were trampled or were injured jumping fences.
"It was chaos — people just running for their lives. People trying to get down. Trying to get to their loved ones that had gotten hit," Shaun Topper said.
Marie Langer, 16, of Las Vegas, got to the concert early so she could get to the very front, closest to the stage.
That meant she and her friends were among the last to get out, and could hear shots ringing and people screaming the entire time she was trying to flee. She finally had to climb a fence with points on the top of metal bars designed to prevent people from getting over it.
"We had no other option," she said.
Tales of heroism and compassion emerged: One man grasped the hand of a dying stranger, unable to pull himself away despite the danger. Another borrowed a flannel shirt from a man he didn't know to create a tourniquet for a girl he didn't know.
Couples held hands as they ran. The healthy carried the bleeding off the grounds. Strangers drove victims to hospitals in their own cars.
Authorities put out a call for blood donations and set up a hotline to report missing people and speed the identification of the dead and wounded. They also opened a "family reunification center" for people to find loved ones.
Before Sunday, the deadliest mass shooting in modern U.S. history took place in June 2016, when a gunman who professed support for Muslim extremist groups opened fire at a gay nightclub in Orlando, Florida, killing 49 people.
Sally Ho, Regina Garcia Cano and Brian Skoloff in Las Vegas; Brian Melley and Andrew Dalton in Los Angeles; Sadie Gurman and Tami Abdollah in Washington; Kristin M. Hall in Nashville, Tennessee; and Jocelyn Gecker in San Francisco contributed to this report.