Stephen Paddock, 64, killed at least 59 people and injured a further 527 when he fired on concert-goers from the vantage point of a 32nd-floor hotel room in Las Vegas.
Armed with as many as 23 weapons, including semi-automatic rifles, Paddock opened fire at 10.08pm on Sunday (5.08am UK time) in a shooting spree that lasted between five and 10 minutes.
As police prepared to storm his hotel room, Paddock committed suicide by turning one of the guns on himself.
With the motive still unknown, police were scouring Paddock’s personal life for clues.
Joseph Lombardo, the local sheriff for Clark County, said a search of the suspect’s car turned up a supply of ammonium nitrate, a fertilizer compound that can be used in explosives. It was used in the 1995 truck bombing of the Alfred P. Murrah Federal Building in Oklahoma City that killed 168 people.
Police found another 19 firearms, some explosives and thousands of rounds of ammunition at his home in Mesquite, along with “some electronic devices that we are evaluating at this time,” Mr Lombardo told reporters.
Police obtained a warrant to search a second house connected to Paddock in Reno, Nevada, more than 400 miles northwest of Las Vegas, Assistant Sheriff Todd Fasulo later told reporters.
Chris Sullivan, the owner of the Guns & Guitars gun shop in Mesquite, issued a statement confirming that Paddock was a customer who cleared “all necessary background checks and procedures,” and said his business was cooperating with investigators.
“He never gave any indication or reason to believe he was unstable or unfit at any time,” Sullivan said. He did not say how many or the kinds of weapons Paddock purchased there.
Isil repeatedly said it was responsible for the attack, claiming that Paddock had converted to Islam in the past few months. The terrorist group described him as a “martyr”, who was using the Arabic name Abu Abdul al-Bar al-Amriki. Both police and the FBI said they were still seeking a motive and added that Paddock was not known to be connected to any terrorist group.
Police said Paddock had checked into the Mandalay Bay Resort and Casino Hotel on Thursday and then waited until the final act of the last night of a three-day country music festival when crowds were at their peak.