The first shots came at 10:08 p.m., about 20 minutes into a performance by country-music star Jason Aldean. More than 22,000 concert-goers sought cover as a barrage of what sounded like automatic weapons fire ripped through the crowd, fired from a room on the 32nd floor of the Mandalay Bay hotel across the street.
Police said the suspect, 64-year-old Stephen Paddock, a resident of Mesquite, Nev., had smashed the windows with a hammer-like tool before opening fire. By the time a SWAT team burst into the room, Paddock had killed himself _ leaving at least 10 rifles in his hotel room.
"Right now we believe it's a solo act, a lone wolf attacker," Clark County Sheriff Joe Lombardo said. "We are pretty confident there is no longer a threat." The Las Vegas Metropolitan Police Department is a joint city-county force headed by the sheriff.
Lombardo said authorities had no evidence of a motive. "We don't know what his belief system was at this time."
White House press secretary Sarah Huckabee Sanders grew emotional as she read a statement praising the people who aided victims in the middle of the gunfire. "What these people did for each other says far more about who we are as Americans than the cowardly acts of a killer ever could," Sanders said, quoting from the Bible's Gospel of John: "There is no greater love than to lay down one's life for a friend."
The militant group Islamic State issued a statement claiming responsibility for the attack, saying the gunman had converted to Islam months ago, though it provided no proof; almost immediately, the special agent in charge of the FBI's field office in Las Vegas, Aaron Rouse, said federal authorities had found no such evidence.
"We have determined, to this point, no connection to an international terrorist group," Rouse said.
"It was an act of pure evil," President Donald Trump said in a televised statement in Washington. The president did not refer to the shootings as an act of terrorism, but said he would travel to Las Vegas on Wednesday _ a day after he visits victims of another tragedy, this one the aftermath of Hurricane Maria in Puerto Rico _ to meet with first responders and families of the victims.
"We cannot fathom their pain, we cannot imagine their loss. To the families of the victims, we are praying for you, and we are here for you, and we ask God to see you through this very dark period," Trump said.
"Our unity cannot be shattered by evil, our bonds cannot be broken by violence," Trump added, saying that while Americans may be angry, "it is our love that defines us today and always will forever."
Trump, accompanied by his wife, Melania, Vice President Mike Pence and wife, Karen, and a military honor guard, later led a somber moment of silence for the massacre victims on the White House lawn.
Investigators have begun the massive task of identifying all the dead and wounded while also trying to learn what motivated Paddock, an accountant and licensed pilot who appears to have had no previous run-ins with the law.
That stands in contrast to his father, who was once on the FBI's most-wanted list for bank robbery, Paddock's brother, Eric Paddock, said in an interview in Orlando, Fla.
Police raided Paddock's home where he lived with his girlfriend, Marilou Danley, in a small retirement community called Sun City Mesquite, tucked among meandering roads and single-story homes.
Mesquite police said they'd had no prior contact with the gunman _ no traffic stops, no citations, "no arrests, nothing," Mesquite Police Department spokesman Quinn Averett said. "It's a newer home, a newer subdivision, a nice clean home, nothing out of the ordinary."
Danley was out of the country when the attack happened but is a "person of interest" in the investigation, Lombardo said. Officials have contacted her and plan to question her when she returns to the U.S.
The gunman's brother said he was "dumbfounded" by the attack.
"Where the hell did he get automatic weapons? He has no military background or anything like that," Eric Hudson Paddock told CBS News in Orlando. "He's a guy who lived in a house in Mesquite and drove down and gambled in Las Vegas. He did ... stuff. Ate burritos. I mean _ "
Paddock turned away in disgust.
"No religious affiliation. No political affiliation. He just hung out," he said of his brother.
Their father, Benjamin Hoskins Paddock, was wanted on bank robbery charges and was arrested in Las Vegas in 1960, Eric Paddock said in an interview. He tried to run an FBI agent over with his car before he was captured, according to news accounts from the time.
The elder Paddock, who had a wife and four children in Arizona, was placed on the most-wanted list after escaping from a federal prison in La Tuna, Texas, on Dec. 31, 1968, having served eight years of a 20-year sentence.
He was captured in Springfield, Ore., in 1978, having opened a bingo parlor for a nonprofit organization in Eugene, Ore., during his time on the lam. He died in 1998.
Paddock's former brother-in-law, Scott Brunoehler, remembers the gunman as a smart, fun-loving person.
Paddock was a young man thriving in Southern California when he was married to Brunoehler's sister, Sharon, in the 1970s and early 1980s, Brunoehler said in an interview.
"Oh, he was a smart guy, like an accountant or something. He had a good job, he was a great guy actually," Brunoehler said. "We used to go water skiing together."
Brunoehler, 62, said he hasn't spoken to Paddock since he divorced his sister.
"It was pretty mutual, they just kind of grew apart," Brunoehler said.
When they were in their 20s and 30s, Paddock would take them out on his boat at Castaic Lake or Buena Vista Lake in Kern County, Brunoehler said.
"He seemed like a normal, good guy. I don't remember anything bad back then at all," he said. "I'm still in shock."
Previously, the worst mass shooting in modern American history was the June 12, 2016, massacre at the Pulse nightclub in Orlando. That shooter, Omar Mateen, had pledged his allegiance to Islamic State.
With the massacre at Virginia Tech in 2007 _ where 32 people were killed by a mentally disturbed student _ the three deadliest shootings in nearly a century have all happened within the past 10 years.
The three-day Route 91 Harvest country music festival was underway across Las Vegas Boulevard from the Mandalay Bay when the shooting erupted about four or five songs into Aldean's performance.
"Single shot. Single shot, then a lot of shots," concert attendee Frank Allard said. Many concertgoers didn't initially realize what was going on.
"I thought it was like bottle rockets going off," said Seth Bayles, of West Hollywood, Calif., who was about 50 feet from the stage. "Then we saw people dropping. We saw someone get hit and then we started running."
Dozens of people dropped to the ground, screaming, while others ran, some in pairs or in groups with their arms linked. The shooting went on for more than 30 seconds before the music stopped, and another burst was heard later. Aldean and the band were pulled off stage.
"Get down, stay down," one woman shouted in a video posted to social media. "Let's go," another voice said. Another wave of gunshots followed soon after.
Allard said the crowd began to stampede and he grabbed a nearby fence, stretched both arms wide and tried to shield his wife from the danger. Then they ran.
"We followed the crowd out," said his wife, Bernice Allard.
Two men near Mandalay Bay said they heard someone in a helicopter with a bullhorn yelling, "Go! Go! Go!" as the incident unfolded. Others said they saw police and SWAT teams streaming into the hotel, where police said they coordinated with hotel security to narrow down what floor the gunman was on, after which his room was easy to find.
Many of the concert's attendees were off-duty law enforcement officers who had gone to the show for a good time.
One of the dead was an off-duty police officer who was attending the concert, Lombardo said. Several other officers from Nevada and California, both on and off duty, were wounded by gunfire, officials said.
Several off-duty police officers from Bakersfield, Calif., were among those attending the concert when the gunfire began. Bakersfield Police Lt. Jeff Burdick said they were not in a position to return fire.
One Bakersfield officer was wounded by the gunfire and was taken to a hospital for treatment, but is expected to survive, Burdick said.
Two young prosecutors were near the stage when the shooting happened and remained "pretty shaken up," said Clark County District Attorney Steve Wolfson. "This is a classic WMD _ a weapon, and a man, of mass destruction."
"A tragic and heinous act of violence has shaken the Nevada family," Gov. Brian Sandoval said on Twitter. "Our prayers are with the victims and all affected by this act of cowardice."
Both Trump and California Gov. Jerry Brown ordered flags flown at half-staff. "Our prayers and deepest sympathies are with the families and loved ones of those killed and injured in last night's tragic and senseless shooting and we stand with the people of Nevada in this difficult time," he said in a statement.
At University Medical Center early Monday, Mason Van Houweling, the hospital's CEO, stood outside with the officers, his face weary. He'd been there since just after the shooting.
There was blood everywhere, he said, all near the entrance. People were coming in ambulances, in taxis. Some drove strangers with bullet wounds. Some, wounded, drove themselves. Hospital staff started doing triage in the parking lot and the entrances to the hospital.
"Our team has done miraculous work in a very tense situation," Van Houweling said.
Hospital staff just started showing up to work, unasked, he said. Medical professionals who were in town visiting showed up. There were two anesthesiologists from Florida. A number of nurses were from out of state.
His eyes grew cloudy.
"It's like a bad dream," Van Houweling said. "This happened to so many nice people. It was a country music festival _ so many people who are so warm."
Authorities established a command post and triage center, and shut down parts of the Strip in the hours after the shooting. Hotel guests blocked from returning to their hotels were shuttled to a center equipped with metal detectors.
Police initially investigated reports of a "suspicious device" down the street, outside the Luxor Hotel, but said later there appeared to be no explosive devices related to the incident, other than that used by the SWAT team breaching the room where the suspect was.
Officials at McCarran International Airport reported that some flights were diverted in the immediate aftermath of the shootings. "Expect delays," the airport said on Twitter.
Parts of Interstate 15 near the Strip were also shut down, and hotel guests across the city were being ordered to shelter in place. The freeway reopened later, but off-ramps near the Strip remained closed through much of the night.
Aldean was the final act of the Route 91 Harvest festival, while dozens of others had played over the course of the weekend. In numerous tweets, artists communicated with fans and followers, expressing their sorrow and prayers for anyone injured and telling loved ones that they were safe.
Jake Owen, who played the main stage before Aldean, tweeted: "Praying for everyone here in Vegas. I witnessed the most unimaginable event tonight. We are okay. Others aren't. Please pray."
Aldean responded on Instagram:
"Tonight has been beyond horrific," he wrote. "I still don't know what to say but wanted to let everyone know that Me and my Crew are safe. My Thoughts and prayers go out to everyone involved tonight. It hurts my heart that this would happen to anyone who was just coming out to enjoy what should have been a fun night. #heartbroken #stopthehate."
Los Angeles Times staff writer Hailey Branson-Potts reported from Las Vegas and Alene Tchekmedyian and Matt Pearce from Los Angeles. Times staff writers David Montero and Ruben Vives in Las Vegas, Joseph Serna in Los Angeles, and Orlando Sentinel reporters David Harris and Michael Williams contributed to this report.