Mesquite, Nevada (CNN) He seemed so ordinary, just another house-hunting retiree, when he strolled with his girlfriend into the sales office of the Sun City development in late 2014. The agents had just what Stephen Craig Paddock was looking for -- a 2,000-square-foot, two-bedroom stucco rambler on a cul-de-sac.

Other houses might offer bigger floor plans, but the one on Babbling Brook Court had two big selling points: a commanding hilltop view and, perhaps most importantly, privacy. Neighbors lived to the left and right, but none behind the home. Paddock quickly said he'd take it.

He stood about 6-foot-4 but came across as "low key and relaxed, a good guy," one of the real estate agents recalled, speaking on condition of anonymity. Balding and paunchy, Paddock was the opposite of flashy. On his application, he said his income came from "gambling." He gambled about $1 million a year, he told one of the agents.

And he paid cash for the house, the agents said -- $369,022.

Soon, Paddock set about making alterations to his pumpkin-colored ranch. And his deep desire for privacy had the opposite effect: It drew the attention of neighbors.

Paddock erected a solid mesh privacy screen that blocked his neighbors' view of his home. About 20 of them signed a petition, and the homeowner's association ordered him to take it down, neighbors said. The HOA refused to comment.

Neighbor Scott Smith said he couldn't understand why anyone would want to obscure a gorgeous view of the town below. "Why would you not have that lot for the view? Obviously, he wanted privacy."

Another neighbor said Paddock told her, "I don't want to be looking at people, and I don't want people looking at me."

With the exception of that neighborhood squabble, Paddock appeared to be good at keeping a low profile. So good, in fact, he managed to assemble a sizable arsenal apparently without notice. And he carted at least 10 suitcases and 23 guns to the 32nd floor of the Mandalay Bay Resort and Casino in Las Vegas last week without raising an eyebrow.

There, he executed a meticulous plan. The man who sought privacy and kept a low profile became the worst mass shooter in modern US history.

Stephen Paddock and his girlfriend, Marilou Danley.

As the police investigation enters another day, details are emerging about how Paddock -- a man with no criminal record or military experience -- carried out such an awful and bizarre mission. Investigators have yet to answer the most troubling question: Why?

Police and federal authorities say they found about four dozen firearms in three locations -- 23 in Paddock's hotel room, seven at a home in Reno and 19 at his house on the cul-de-sac in Mesquite. They also found ammonium nitrate, which is used in bombmaking, in his car and in Mesquite.

The woman he shared those homes with, Marilou Danley, was in the Philippines at the time of the massacre but returned to Los Angeles and met Wednesday with the FBI.

Afterward her lawyer read a statement from Danley. She said she was completely unaware of Paddock's deadly plan and is cooperating with investigators. She said Paddock found her a cheap plane ticket to visit family in the Philippines and confirmed that he wired her money to buy a house. Danley said she believed he was breaking up with her.

The couple's Mesquite real estate agent, meanwhile, finds it almost impossible to square the mild-mannered man to whom she sold a home with the now-notorious mass murderer. "Trust me when I say there's a place in hell for this guy," she said.

Rarely seen

Window treatments at Paddock's house on Babbling Brook Court made it hard to see inside. His neighbor, Scott Smith, knew he was a gambler, and assumed he slept during the day.

Danley was pleasant, Smith said; Paddock, not so much. He wouldn't wave back. He seemed to have tunnel vision, to be in his own world.

Not that there was a lot of neighborly interaction. "Garage is up. They're in the house. Garage is down. That was about it," Smith said.

The same appeared to be true in other places where Paddock had a house. Neighbors near his homes in Reno and Melbourne, Florida, said they rarely saw him.

Don Judy lived next door to Paddock in Florida. He said Paddock's house there was sparsely but tastefully furnished. Paddock rented a car every time he visited, about half a dozen times over two years, Judy and his wife told CNN.

Paddock didn't seem as interested in privacy as he'd been in Mesquite; he handed Judy a house key and told him he could borrow a ladder or lawn equipment if he kept an eye on the place. Paddock said he was a high roller and real estate speculator from Las Vegas. "We're up all night because we gamble," Judy remembered him saying.

People who thought they knew Paddock said they were completely unaware of his gun collection. Authorities say he purchased 33 of his firearms, most of them rifles, over the past year.

Judy called him "a gentle giant" and said he had trouble even picturing him holding a gun.

Stephen Paddock's home in Mesquite, on October 3, after the Las Vegas massacre.

"If there was any impression, I would say the guy had no idea what a gun was," he said. "He was very simplistic. If I could say, impression of it was 'gentle giant,' he just never showed any kind of aggression or anything."

Location, location, location

Records show Paddock's knack for investing in real estate first developed when he was still a young man working as a postal worker. Besides the Nevada properties, records link him over the years to nine other houses, condos and apartment buildings.

While he took an $11,000 hit on the Florida house when he sold it, the records show Paddock bought and sold another property in Reno, two homes and an apartment complex in Mesquite, Texas, and at least four other properties in California. He profited handsomely from the sale of an apartment building he owned with a former wife and other family members. The building, purchased in 1992, sold for $3.2 million in 2004.

Eventually, around 2012, Paddock began spending more time in Reno, and sticking to his pattern, began buying property there. He also found a girlfriend. Although it is not yet clear how they met, Marilou Danley's job might have been the connection. An Australian citizen and former airline hostess and Avon sales representative, she worked for a time as a hostess to high-limit gamblers at Club Paradise at the Atlantis Casino Resort Spa.

Paddock's brother, Eric, has met Danley, and described the couple as devoted to each other. He told the Washington Post that Paddock once treated the whole family to a gambling vacation, taking over the penthouse floor at the Atlantis at the casino's expense.

He might have kept quiet about the guns, but he wasn't shy about the gambling.

"He gambled because it was fun," Eric Paddock told CNN. "Because you're in a place where there's ringing bells and 'Surprise, surprise!' It was fun because people were nice to him. Girls brought him drinks. They served him big shrimp. I mean, he liked to gamble, and they put him up in crazy hotel rooms."

A former bartender at Peggy Sue's restaurant recalled serving Paddock and his girlfriend in recent years.

"They were quiet. They just sat there by themselves," said the woman, who works in a different field now and asked that her name not be used.

She said there was one thing in particular she recalled in light of news reports that he was wealthy.

"He wasn't a heavy tipper," she said. "I know that. That I would remember."

Others who regularly dealt with Paddock and Danley saw a dark side.

A barista at a Starbucks at the Virgin River Casino in Mesquite told the Los Angeles Times that he rudely berated her in public. And, he glared at Danley when she asked to use his casino card to buy food or drinks.

"He would glare down at her and say, with a mean attitude, 'You don't need my casino card for this. I'm paying for your drink, just like I'm paying for you.'"

And yet, he seemed to have no qualms about using her casino card in his final days.

Leaked photos published by the Daily Mail show the scene, including what appears to be the shooter's body, inside Stephen Paddock's room at the Mandalay Bay in Las Vegas.

He reportedly used Danley's slot machine card to gamble at the Mandalay Bay's casino, according to Clark County Commission Chairman Steve Sisolak. It's not clear when he first showed up at the hotel, but he checked into the suite and an adjoining room on the 32nd floor on Thursday, September 28.

And then, shortly after 10 p.m. on Sunday, Paddock apparently swung a heavy hammer to smash out two windows, one in the room and the other in the suite. He opened fire on an unsuspecting crowd attending a country music festival 32 stories below. Round after round hailed down in rapid bursts for nine, 10, up to 11 minutes. It felt like an eternity.

The first frantic 911 call came at 10:05. When the guns fell silent at 10:19, 58 people were dead or dying and nearly 500 others were injured. Paddock peppered the door of his suite with gunfire to keep hotel security at bay, but saved the last bullet for himself.

This article has been updated to reflect authorities' revision of the number of people hurt in the Las Vegas shooting.