(CNN) -- Investigators are still trying to pin down Stephen Paddock's motive for opening fire on thousands of country music fans in Las Vegas, killing 58 people and wounding nearly 500 in the worst mass shooting in modern US history.
What they have uncovered -- in his 32nd-floor suite at the Mandalay Bay hotel, his car, and his homes -- is a remarkable collection of firearms commensurate with the scale of violence he unleashed before he killed himself as police closed in.
Here's what we know about the weapons cache:
In all, authorities have found 47 guns of varying size and power that belonged to Paddock.
Investigators discovered 23 guns in his hotel room in Las Vegas in the immediate hours after the attack, plus another 24 at his homes in Mesquite and Verdi, Nevada, near Reno.
It's not clear how many guns were rifles or handguns. But at least 12 of those in the hotel room were outfitted with bump stocks, which allowed the semi-automatic weapons to mimic the gunfire of automatic ones, according to Jill Snyder, special agent in charge of the ATF's San Francisco field division.
Such a large collection isn't necessarily unusual, Sam Rabadi, a retired special agent for the Bureau of Alcohol, Tobacco, Firearms and Explosives, told CNN
"There are states in the country where there's a lot of hunting, outdoor activities. There are also areas where you have a higher population of collectors," Rabadi said. "The purchase of that many firearms in and of itself don't necessarily raise red flags for us."
Police also discovered more than 50 pounds of exploding targets and 1,600 rounds of ammunition in Paddock's car in the hotel's parking lot.
Paddock was "a man who spent decades acquiring weapons and ammo," Sheriff Joseph Lombardo of the Las Vegas Metropolitan Police Department said during a Wednesday news conference.
But while some of the weapons were bought over the last 20 years, authorities believe 33 of the 47 guns -- most of them rifles -- were purchased between October 2016 and last month, an ATF spokesperson said.
Paddock amassed at least some of his collection from a variety of gun stores throughout the southwestern US. He visited gun stores in Nevada, Utah, California and Texas, where he purchased rifles, pistols and shotguns, Snyder said.
Chris Michel, the owner of Dixie GunWorx in St. George, Utah, remembered selling a gun to Paddock, he told CNN affiliate KTVX.
"(Paddock) didn't set off any alarms. I didn't think there was a problem with him," Michel said. "He came in, he wanted a firearm, he knew exactly what he was looking for. He just wanted a shotgun."
There is no federal limit on how many firearms or how much ammunition someone can buy, and there's no national database that tracks gun purchases.
Federal law does require firearm dealers to conduct background checks on those purchasing weapons, which would check things like criminal history.
Several gun store owners Paddock purchased weapons from told CNN that no red flags were raised during his background checks.
"My staff takes their job very seriously and if there were any red flags during this transaction, like any other, it would be halted immediately," said David Famiglietti of New Frontier Armory in Las Vegas, where Paddock purchased a shotgun and a rifle this spring.
Richard Vasquez, the former chief of firearms technology for the ATF, said the fact that Paddock was able to purchase 33 guns should tell us "he had a very clean background."
"For a person to purchase 33 firearms -- and in different states -- there would be, in my opinion, absolutely no way it would have passed 33 checks if he had something in his background," Vasquez said.
Background checks for gun purchases are run against the National Instant Criminal Background Check System (NICS), developed by the FBI, that hits military, state and federal databases, as well as mental health records. Vasquez called it "a very comprehensive background check."
Again, there's no national database that keeps track of gun purchases, but the ATF does require federal firearm licensees to report the purchase of multiple handguns by the same purchaser, as mandated by the Gun Control Act of 1968.
The sales "must be reported if they occur at the same time, or within five consecutive business days of each other," the ATF's website says.
Some states, such as California, regulate how often guns can be purchased. In that state, a buyer can only apply to buy a handgun once every 30 days. New York City takes that a step further, limiting purchases to once every 90 days, according to the Law Center to Prevent Gun Violence.
There is no such law in Nevada, where Paddock lived, nor is a buyer required to have a permit to buy a gun. The state also has no laws regulating assault weapons.
But Vasquez notes there's no equivalent federal requirement for reporting multiple purchases of long guns like rifles or assault weapons. That means the ATF and other law enforcement agencies never caught wind of Paddock's rifle purchases.
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