On October 1, 2017, a mass shooting occurred when 64-year-old Stephen Paddock opened fire on the crowd attending the Route 91 Harvest music festival on the Las Vegas Strip in Nevada from his 32nd-floor suites in the Mandalay Bay hotel.

[6] Las Vegas Village, a 15-acre (6-hectare) lot used for outdoor performances, was located diagonally across the intersection to the northeast and owned by MGM Resorts International.

[7][8][b] Stephen Paddock was a 64-year-old former auditor and real estate businessman who had been living 80 miles (130 km) northeast of Las Vegas in a retirement community in Mesquite, Nevada.

[15] According to his girlfriend, Paddock repeatedly cased Las Vegas Village from different windows in their room when they stayed at the Mandalay Bay a month before the shooting.

Twenty-four firearms, a large quantity of ammunition, and numerous high-capacity magazines capable of holding up to 100 rounds each were found in the suite.

[21][22] Fourteen of the firearms were .223-caliber AR-15-type semi-automatic rifles: three manufactured by Colt, two by Daniel Defense, two by FN Herstal, two by LWRC International, two by POF-USA, one with a .223 Wylde chamber by Christensen Arms, one made-to-order by LMT, and one by Noveske.

[21][23][24] All 14 of the AR-15 rifles were fitted with vertical forward grips and bump stocks,[21][23] the latter of which allowed for recoil to actuate their triggers at a rate of 90 rounds in 10 seconds.

[40][41][42][43] After Paddock used a hammer to break two of the windows in both of his suites,[8] he began shooting through them at 10:05 p.m.[44] He ultimately fired over 1,000 rifle rounds[28] approximately 490 yards (450 m) into the festival audience.

[49][50] In addition to shooting at the concertgoers, Paddock fired eight bullets at a large jet fuel tank at McCarran International Airport 2,000 feet (600 m) away.

[51] During the shooting, police officers were initially confused whether the shots were coming from the Mandalay Bay, the nearby Luxor hotel, or the festival grounds.

[54][55] Police then breached Room 32–134; while entering the hotel suite, an officer accidentally fired a three-round burst from his weapon, but the bullets did not hit anyone.

[64][65] Thirty-four were from California; six from Nevada; four from Canada; two each from Alaska and Utah; and one each from Arizona, Colorado, Iowa, Minnesota, Massachusetts, New Mexico, Pennsylvania, Tennessee, Washington, West Virginia, and Wisconsin.

[89] Brittany Speer, an EMT at UCLA, received a Medal of Courage from the University of California Police Department (UCPD) for her bravery in setting up a triage area and treating victims while the shooter was still active.

[91] Matthew Cobos, a U.S. Army soldier, received the 2018 Single Act of Heroism Award from the Congressional Medal of Honor Society for shielding and providing life saving medical treatment to injured concert-goers.

Detective Michael Vo and Officers Thomas McGrath, Mark Williams, Max Verduzco and Richard Barton received the Medal of Valor for their actions in treating the wounded, creating escape routes, and shielding concert-goers.

Detective Scott Gosnell and Officers Caitlin Milligan, Eric Hansen, Bryan Johnson, William Hernandez Jr. and Braden Wilson received the department's "Exceptional Performance Citation" for assisting concert-goers and helping them escape the venue.

[103] Police said a handwritten note found in the room indicated Paddock had been calculating the distance, wind, and trajectory from his 32nd floor hotel suite to the concertgoers he was targeting on the festival lot.

[104][105] At a press conference on October 4, Clark County Sheriff Joe Lombardo stated there was evidence—which he declined to discuss—that Paddock intended to escape the scene, and that he may have had assistance from an accomplice.

[37] In their first statement about the incident, police officials inaccurately reported that Campos arrived on the scene after Paddock began firing into the crowd.

That report had been based on a 9:59 p.m. notation in a hotel security log, which in a third statement was determined to have been the time when Campos encountered the barricaded door.

[36][38] Sheriff Lombardo dismissed allegations that the changing timeline was the result of some kind of conspiracy between the police department, the FBI, and MGM Resorts International saying, "Nobody is attempting to hide anything in reference to this investigation.

[110] On August 3, 2018, Clark County Sheriff Joe Lombardo held a press conference on the release of the LVMPD Criminal Investigative Report of the October 1 Mass Casualty Shooting.

[128][129] Political scientist Joseph Uscinski suggested the removal of this content ironically fuels conspiracy theories by making a cover-up seem evident.

[131]At a press conference, U.S. President Donald Trump described Paddock as "a very very sick individual", and "a demented man, [with] a lot of problems" and described the event as an "act of pure evil".

The event received a massive amount of security, which included counter-sniper surveillance posts; 350 police officers; and a number of barriers composed of dump trucks, buses, and other large vehicles.

[139] The expansion Vegas Golden Knights of the NHL held a tribute to the victims and honored response personnel before their inaugural home game on October 10.

[146][147] In March 2019, Las Vegas police officer Cordell Hendrex, who did not immediately respond to the gunfire but had remained in the floor below Paddock, was fired for his inaction.

[153] In December 2018, Acting United States Attorney General Matthew Whitaker signed a regulation banning bump stocks in the U.S., effective March 2019.

[158][159] In November 2017, a lawsuit was filed on behalf of 450 of the victims of the shooting, which claimed that the Mandalay Bay Hotel had shown negligence by allowing Paddock to bring a large amount of weaponry into the building.

The case was finally decided in his favor on 14 June 2024 by a majority opinion from the US Supreme Court that bump stocks should not be considered as machine guns in the meaning of the law.