Officers were able to determine the shots were coming from the 32nd floor of the hotel, and they stormed the room and found the suspect had killed himself, authorities said.
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Paddock was found dead in the hotel room with as many as 10 firearms. Authorities said he likely killed himself before officers made entry.
The gunman is of Mesquite, Nevada, just outside of Las Vegas. They described him as a "lone wolf" and do not believe there are other suspects involved in the shooting.
The Islamic State has claimed the Las Vegas attack, saying Paddock converted to Islam months ago, but they did not provide evidence. Investigators in Las Vegas also have not found evidence of ties to terrorism.
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IS often claims attacks by individuals inspired by its message but with no known links to the group.
"We are pretty confident that there is no longer a threat," said Sheriff Joseph Lombardo with the Las Vegas Metropolitan Police Department.
A woman described as a roommate and traveling companion of Paddock, identified as Marilou Danley, was initially sought as a person of interest. After detectives spoke with her, they determined she was not involved with the shooting.
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Officials said they continue to seek a vehicle registered to Paddock, described as a Hyundai Tucson with Nevada plate 114-B40. A Chrysler Pacific Touring minivan with Nevada plate 79D401 also connected to him was found. (The Chrysler plate was initially listed incorrectly by police at an early morning press conference, but the plate was later updated).
Singer Jason Aldean was just finishing up his set at the Route 91 country music festival when a series of shots - about 200 rounds within 4 1/2 minutes - were fired in rapid-fire bursts, witnesses said. About 22,000 people were in attendance.
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Terrified concertgoers ran for cover and described a scene of mass chaos as people were felled by bullets and friends tried to help them at the scene.
"It was the craziest stuff I've ever seen in my entire life," 36-year-old Kodiak Yazzie said. "You could hear that the noise was coming from west of us, from Mandalay Bay. You could see a flash, flash, flash, flash."
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Aerial footage from the strip shows a window shot out at the Mandalay Bay hotel, appearing to be the room where the gunman opened fire on the crowd below. Investigators were seen inside the room Monday morning.
As news of the shooting spread, rumors of multiple shooters at multiple locations spread through social media. Police later dismissed those reports, saying there was one shooter at one location. There were also no explosives involved, other than those used by the SWAT team to enter the suspect's hotel room, Lombardo said.
A tragic & heinous act of violence has shaken the #Nevada family. Our prayers are w/ the victims & all affected by this act of cowardice.— Governor Sandoval (@GovSandoval) October 2, 2017
In the initial chaos, authorities shut down part of the Las Vegas Strip and the 15 Freeway.
A groundstop was initiated for Las Vegas' McCarran International Airport for departing and arriving flights. Flights were allowed to resume less than two hours later, but travelers were advised to check with their airlines as some delays were possible.
Among the dead is a Las Vegas police officer, authorities confirmed.
According to the LAPD's Foothill Division, one of their officers was attending a country music festival at the resort on the Las Vegas strip when shots rang out, causing panicked concertgoers to flee from the outdoor venue.
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The female LAPD officer, who was attending the concert with friends, was shot in the knee. She is in stable condition, police said.
The Bakersfield police department said several of its officers were off-duty attending the concert and at least one was struck by a bullet. The officer was being treated at a hospital with non-life-threatening wounds.
President Donald Trump extended his condolences to the victims of the shooting in Las Vegas and their families.
My warmest condolences and sympathies to the victims and families of the terrible Las Vegas shooting. God bless you!— Donald J. Trump (@realDonaldTrump) October 2, 2017
White House spokeswoman Sarah Huckabee Sanders said Trump was "briefed on the horrific tragedy in Las Vegas."
Sanders said that "we are monitoring the situation closely and offer our full support to state and local officials. All of those affected are in our thoughts and prayers."
Las Vegas Mayor Carolyn Goodman tweeted a brief statement: "Pray for Las Vegas. Thank you to all our first responders out there now."
Nevada Gov. Brian Sandoval tweeted: "A tragic & heinous act of violence has shaken the #Nevada family. Our prayers are w/ the victims & all affected by this act of cowardice."
Click here for full coverage on the Las Vegas mass shooting.
We're investigating reports of an active shooter near/around Mandalay Bay Casino. Asking everyone to please avoid the area. #LVMPDnews— LVMPD (@LVMPD) October 2, 2017
Shooting in Las Vegas. People fleeing (video from the Mandalay Bay hotel) pic.twitter.com/hs98J5uK6T— Eiki Hrafnsson (@EirikurH) October 2, 2017
Pray for Las Vegas. Thank you to all our first responders out there now.— Carolyn G. Goodman (@mayoroflasvegas) October 2, 2017
ABC News and the Associated Press contributed to this report.