The Las Vegas gunman who killed 58 people and himself in the deadliest mass shooting in modern U.S. history stockpiled weapons and ammunition over decades, and meticulously planned the attack, authorities believe.
But what led Stephen Paddock, 64, to unleash the carnage he did remains largely a mystery.
"What we know is that Stephen Paddock is a man who spent decades acquiring weapons and ammo and living a secret life, much of which will never be fully understood," Clark County Sheriff Joseph Lombardo said at a news briefing on Wednesday night
Lombardo said he found it hard to believe that the arsenal of weapons, ammunition, and explosives recovered by police in their investigation could have been assembled by Paddock completely on his own.
"You have to make an assumption that he had some help at some point," Lombardo said.
Some 489 people were also injured when Paddock strafed an outdoor concert with gunfire on Sunday night from his 32nd-floor suite of the Mandalay Bay hotel on the Las Vegas Strip. He then took his own life.
There is evidence that Paddock tried to survive and escape. He also may have scouted out the location, renting a room at the Ogden, a nearby hotel, during the Life is Beautiful festival a week earlier, Lombardo said.
Police recovered nearly 50 firearms from three locations they searched, nearly half of them from the hotel suite. Twelve of the rifles there were fitted with so-called bump stocks, officials said, allowing the guns to be fired almost as though they were automatic weapons.
Lombardo said investigators were examining the possibility Paddock's purchase of more than 30 guns in October 2016 may have been precipitated by some event in his life. He did not elaborate.
There remained no evidence as yet "to indicate terrorism" in the shooting spree, said Aaron Rouse, FBI special agent in charge of the Las Vegas field office.
Paddock's girlfriend Marilou Danley was questioned by the FBI on Wednesday and said in a statement she was unaware of the Paddock's plans.
"He never said anything to me or took any action that I was aware of that I understood in any way to be a warning that something horrible like this was going to happen," Danley, 62, said in a statement released by her lawyer Matt Lombard.
Danley returned late on Tuesday from a family visit to the Philippines. She is regarded by investigators as a "person of interest." Lombard said his client was cooperating fully with authorities.
A Federal Bureau of Investigation official in Las Vegas, meanwhile, said no one has been taken into custody.