LAS VEGAS — Investigators were trying to determine the motive for a wealthy, retired accountant's heinous shooting rampage while the city and nation struggled Tuesday to heal from the most deadly mass shooting in modern U.S. history.

At a late-night press conference Tuesday, authorities said Stephen Paddock made his attack even more deadly by adding more lethal components to his weapons. He had devices attached to 12 semiautomatic rifles that allowed them to mimic fully automatic gunfire.

Bureau of Alcohol, Tobacco and Firearms Special Agent in Charge Jill Schneider also told reporters Tuesday that Stephen Paddock had nearly 50 guns in three locations.

She said he had a combination of rifles, shotguns and pistols.

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The gun attachment that mimics automatic gunfire is a little-known device called a “bump stock” that was not widely sold. The stocks have been around for less than a decade, and Schneider said officials determined they were legal.

President Trump, as he left Washington for a trip to storm-ravaged Puerto Rico, briefly referenced Paddock, whose carnage Sunday night left 59 people dead and more than 500 injured.

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"He was a sick man, a demented man with a lot of problems, I guess, and we are looking into him very, very seriously," Trump said. "We are dealing with a very, very sick individual."

The president also said the administration would be "talking about gun laws as time goes by," and he lauded the efforts of Las Vegas law enforcement.

"How quickly the police department was able to get in (to Paddock's hotel room) was very much a miracle," he said. "They've done an amazing job."

While Paddock's motive remains unclear, authorities were putting together a more complete picture of his work history and his past. The killer worked as a letter carrier for the U.S. Postal Service, an IRS agent and in an auditing department over a 10-year period.

A spokeswoman for the Office of Personnel Management told The Associated Press on Tuesday that Stephen Paddock’s employment included about two years as a mail carrier from 1976 to 1978.

After that, he worked as an agent for the Internal Revenue Service for six years until 1984. And then he worked a defense auditing job for about 18 months.

He graduated from college in 1977 from Cal State Northridge and also worked for a defense contractor in the late 1980s.

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Country music star Jason Aldean was performing when Paddock opened fire from the window of his 32nd-floor hotel room overlooking the Route 91 Harvest music festival. Aldean, who was not injured, tweeted a statement Tuesday saying he has been overwhelmed with emotion since the attack.

"Something has changed in this country and in this world lately that is scary to see," Aldean wrote. But he also added that it is "time to come together and stop the hate."

Stories of heroism continued to emerge. One minute Marine veteran Taylor Winston was dancing the two-step at the concert, the next he was commandeering a pickup and shuttling the wounded to hospitals before ambulances arrived. Dawn-Marie Gray, a concertgoer who happened to have seven years experience as a paramedic, found herself providing CPR and tying tourniquets.

When Nick Jones, 30, of Vancouver, Wash., heard about the shooting, he drove 20 hours to help. He offered to donate blood, but the need had been met. He offered to volunteer at hospitals, but they had plenty of help. Even the family assistance center was overwhelmed with volunteers.

“I was worried that no one would do anything,” Jones said Tuesday. “I was happy to be proven wrong.”

Assistant Sheriff Todd Fasulo pleaded for patience during the investigation, saying authorities were "hunting down" every clue to learn more about Paddock.

Several minutes after the carnage began, officers who blasted into the room found Paddock's body. His brother Eric, who lives in Florida, says his multimillionaire brother was a big spender at casinos and often received free meals and rooms there. Eric Paddock also said he believed his brother owned a couple guns.

Police found 23 guns, including semiautomatic rifles, in Paddock's room at the Mandalay Bay Resort and Casino. They found 19 more at his home in Mesquite, Nev., 80 miles northeast of here. And in yet another home owned by Paddock in Reno, authorities found five handguns, two shotguns, and a plethora of ammunition.

A federal law enforcement official, who was briefed on the matter but not authorized to comment publicly, said police also found two tripods positioned at the hotel windows in what appeared to be a fully equipped sniper’s nest.

Las Vegas Sheriff Joseph Lombardo confirmed that some of the shooter's arsenal was modified with technology known as a "bump-stock'' that allows for rapid firing, similar to a machine gun.

The modification, which uses the weapon's natural recoil to fire in rapid succession, is legal, though controversial, as it allows gun owners to bypass machine-gun restrictions that require special permits and fingerprinting.

In addition, investigators believe the gunman set up a surveillance camera for a view of hallway outside his door.

"It was obviously premeditated," Lombardo said. "The fact that he had the type of weaponry and amount of weaponry in that room...I'm pretty sure he evaluated everything he did and his actions, which is troublesome."

While the investigation intensified, authorities touted the city’s resilience in the aftermath of the tragedy. Fully stocked blood banks were soon turning away would-be donors. A GoFundMe page collected $3.3 million from almost 50,000 donors in little more than 24 hours. Overall, donations for the victims have exceeded $3.7 million, Commissioner Stephen F. Sisolak said Tuesday afternoon.

Pieces of normalcy slowly returned to the iconic Strip. Club promoters hawked 2-for-1 deals, tourists took selfies and police cracked down would-be criminals.

“Do you know how disrespectful it is to come out here and deal drugs the day after 50 people died one block away?’’ a bike cop snapped at a man in handcuffs Monday night. “Can’t you take one day off?’’