A shooting during Jason Aldean's performance at the Route 91 Harvest Country Music Festival in Las Vegas on Sunday night left more than 58 people dead and 500 injured, making it the deadliest mass shooting in modern U.S. history. Aldean was performing in front of some 22,000 fans near the Mandalay Bay Resort and Casino around 10:08 p.m. local time when shots were fired. This morning, Las Vegas sheriff Joseph Lombardo said that the shooter, 64-year-old Stephen Paddock of Mesquite, Nevada, is believed to have killed himself before police entered the 32nd-floor hotel room from which he opened fire. (It had previously been reported that Paddock had been killed by a SWAT team.) It's believed that Paddock, who had multiple weapons in his room at the time of the crime, had no prior convictions or run-ins with police and a motive has yet to be determined. Paddock's female roommate was initially suspected of being a co-conspirator, but authorities now believe that he acted alone. Aldean has since written on Instagram, "Tonight has been beyond horrific. I still don't know what to say, but wanted to let everyone know that me and my crew are safe."