By Madison Park, Darran Simon and Philip Victor, CNN
(CNN) -- A day after the deadliest mass shooting in modern US history, authorities are learning more about Stephen Paddock who fired into a crowd of thousands during a country music festival from a Las Vegas hotel room and the weapons he kept.
At least 59 people were killed and 527 were injured in the shooting that started late Sunday night. Police believe he killed himself, ending the massacre.
Police searched the gunman's home in Mesquite, Nevada, where they found at least 19 firearms, explosives, several thousand rounds of ammunition and some electronic devices.
In Paddock's 32nd-floor hotel room at the Mandalay Bay Resort and Casino, police recovered 23 weapons, including a handgun, and multiple rifles -- some had scopes on them. Authorities also found several pounds of ammonium nitrate, a material used to make explosives, in his car.
As police uncovered more evidence, they're still piecing together a motive.
There was no explanation so far on why Paddock, a 64-year-old retired accountant who had never faced any notable criminal charges, unleashed a hailstorm of bullets into concertgoers.
So far, police believe Paddock acted alone.
"We believe Paddock is solely responsible for this heinous act," Clark County Assistant Sheriff Todd Fasulo said in a press conference late Monday.
-- Paddock was alive when he made first contact with officers. A team of six officers spoke with security at the Mandalay Bay Resort and Casino, where Paddock was staying, and searched the hotel floor-by-floor Sunday night before they found Paddock's room, Clark County Sheriff Joseph Lombardo told reporters.
-- Paddock fired at the officers through the door and shot a security guard, Lombardo said. The guard was shot in the leg.
-- A SWAT team broke down the door, but Paddock had already killed himself, he said.
-- Several vigils were held Monday night to honor the victims of the shooting. Community members gathered in Reno, Las Vegas, the Nellis Air Force Base and at the campus of University of Nevada, Las Vegas.
-- Carrie Barnette, a Disney employee, is the latest victim to be identified. "A senseless, horrific, act, and a terrible loss for so many. We mourn a wonderful member of the Disney family: Carrie Barnette," tweeted Disney Chairman and CEO Robert Iger.
-- Paddock bought multiple firearms in the past, but investigators believe the firearms were purchased legally, a law enforcement official said. The official said initial reports suggest at least one rifle was altered to function as an automatic weapon.
-- A North Las Vegas gun store sold a shotgun and a rifle to Paddock in the spring. All state and federal requirements, including a FBI background check, were met, said David Famiglietti, president of New Frontier Armory. He said that neither of the weapons "leaving our store [are] capable of what we've seen and heard in the video without modification."
'There was no cover'
The massacre started about 10:08 p.m. Sunday (1:08 a.m. ET Monday) at the Route 91 Harvest festival, Lombardo said.
Country singer Jason Aldean was performing at the festival attended by 22,000 people when bullets began to rain into the crowd.
Kimberly Folle, who was there, said she heard the gunshots at the beginning of an Aldean song, but didn't think others heard it because the music was so loud.
It sounded like it was coming "from the sky," Folle told CNN's Jake Tapper.
"It's gunshots. It's gunshots. Get down. Get down," she said she told people around her.
The music combined with the gunshots confused many people.
"Some people didn't believe it was real. Some people thought it was fireworks. Some people thought it was a speaker," Rusty Dees, a survivor told Tapper. "Some people were in shock."
Dees and Caren Mansholt were just right of the stage when they heard the shots. At first, Mansholt said she thought it was fireworks, but saw nothing in the sky. Once they started realizing that it was gunfire, Mansholt tried to hide herself under a seat.
"On the main floor, everyone was covering but there was no cover, they were all exposed," Dees said. "So, you didn't know if somebody was shot or if they were laying down."
Many made terrifying dashes to the exits. Frantic concertgoers piled on top of each other, trying to get out of the shooter's line of fire.
In the life-or-death situation, Dees said people were trying to take care of each other.
"It takes the worst of America to also see the best of America. Everybody was helping each other," he said.
Corrine Lomas also recalled the heroism of fellow concertgoers, risking their lives to save others as strangers pulled each other to hide and tended to the injured.
"A lot of really good people (were) holding people's wounds shut, trying to help them while everybody was just ducked down," she said.
"The firing went on forever," another witness Kimberly Chilcote said.
She and her husband ran in short bursts -- sprinting and hiding to avoid being targeted.
"There were purses and shoes everywhere ... there were bodies and blood," she said. "We just kept running."
Taylor Benge said he "could see a guy with a bullet wound right in his neck, motionless," several feet away. "From there on ... people just started dropping like flies."
Who is the shooter?
The massacre has no known link to overseas terrorism or terror groups, a US official with knowledge of the case said.
Police had no prior knowledge of the gunman before the attack, Sheriff Lombardo said. "I don't know how it could have been prevented," he said.
Paddock was divorced with no known children.
The gunman's brother, Eric Paddock in Orlando, Florida, said he was stunned to learn Stephen was believed responsible: "We're still just completely befuddled. Dumbstruck."
He described his brother as having "no history of violence. No history of anything couldn't give a s*** less about politics, religion, pointy hatted people etc, etc. He just wanted to get a freaking royal flush."
He mentioned that his brother "loved to gamble. He loved -- when I say loved -- it was a job. It was fun because people were nice to him."
The last time Eric Paddock spoke to his brother was when Stephen texted him, asking how their mother was doing after losing power from Hurricane Irma.
Eric Paddock said he knew his brother owned a few handguns and maybe one long rifle, but said he didn't know of any automatic weapons.
Hundreds of Nevadans waited in long lines to give blood on Monday, to help victims of the shooting. US blood banks have enough blood to meet the immediate needs after the shooting, according to the chair of the AABB Interorganizational Task Force on Domestic Disasters and Acts of Terrorism, which assesses the need for blood collection after disasters.
People were also donating flights, housing, food, transportation and other goods to victims' family members who are coming to Las Vegas, said Chief Greg Cassell of the Clark County Nevada Fire Department.
Those looking for friends and family still missing after the attack can call 866-535-5654. Facebook has set up a crisis response page to help people determine whether their loved ones are safe.
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