Stephen Paddock, 64, had made millions from real estate deals, according to his brother; he also owned two planes and several properties across the US, and seemed normal apart from his passion for gambling large sums.
But he'd also secretly amassed a massive arsenal of 42 firearms. At least one of those was automatic, while another two had been modified with a legal bump-stock devices that allows semi-automatic guns to give full-auto fire of up to 800 rounds a minute. Several had scopes, and packed military-grade ammunition.
He took 23 of those guns into his Mandalay Bay suite over several days and set up two rifles on tripods at windows overlooking the Route 91 Harvest country music festival.
Thousands of rounds of ammunition were also found in the suite, enabling him to fire repeatedly over the course of 72 minutes. His car had several pounds of a fertilizer used in bomb-making.
Paddock had lived in 27 residences in Nevada, Florida and Texas as an adult, but other than that he had apparently lived a quiet and unremarkable life - and the reason for his assault remains a mystery.
The retired accountant had worked as an internal auditor at Lockheed Martin for three years in the late 1980s, and was a manager and investor in apartment complexes located in Mesquite, Texas and California, which made him millions, according to his brother.
Local police said they had no run-ins with the man, not even traffic violations, and his brother described him as 'just a guy who lived in Mesquite who drove down and gambled in Las Vegas and... liked burritos.'
So the discovery that he had used 10 suitcases to methodically move an arsenal up into his Mandalay Bay room over the preceding weekend came as a shock to those who knew him.
Eric Paddock said he thought his brother was far from a gun fanatic.
'He had a couple of guns but they were all handgun, legal... he might have had one long gun, but he had them in a safe,' he said.
He said he didn't know about the 23 guns that were found in the hotel room. A law enforcement source told the Wall Street Journal that they found at least one fully automatic rifle among the batch, which included AR-15-style rifles and AK-47-style rifles.
And it later emerged that two other semi-auto guns had been legally modified with bump-stocks that allow them to function like fully automatic rifles, pumping out 400-800 bullets a minute.
Bump-stocks replace the gun's shoulder rest with a 'support step' that covers the trigger opening. By holding the pistol grip with one hand and pushing forward on the barrel with the other, the shooter's finger comes in contact with the trigger.
The recoil then causes the gun to buck back and forth, 'bumping' the trigger and firing off multiple shots. But because the finger is technically pulling the trigger each time, it still counts as a semi-auto weapon.
Still others could have been properly converted into fully automatic fire, the LA Times reported. Among the weapons found in the room were four Daniel Defense DDM4 rifles, three FN-15s and other rifles made by Sig Sauer. A handgun was also found.
Clark County Sheriff Joe Lombardo said on Monday it wasn't clear whether the full-auto gun was modified, or if it was originally made that way.
He also said that the ammunition ranged in size from .308, usually used in hunting rifles, to .223, associated with AR-15s and other assault rifles - the latter being military-grade, the New York Daily News reported.
Eric said the revelation of his brother's deadly plan, which saw thousands of rounds falling on a crowd of 22,000 people at a music festival below, was as unexpected as seeing a meteor suddenly landing on his street.
The shocks only grew in number Monday as police raided two of Paddock's properties. The first was his Mesquite home in a sleepy retirement community, which he purchased for just over $369,000 in 2015 according to public records.
What they found was a second arsenal, even bigger than the one in the Mandalay Bay room.
Some 19 additional firearms were in the house, along with the explosive Tannerite - which is used to make explosive targets for target practice - and several thousand rounds of ammunition, Lombardo said Monday.
He added that electronic devices were also found, but that they are still being examined to determine their purpose.
Photos of the property showed the garage door torn off its hinge and crumpled after the search.
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