Greg Palast was stunned when he learned that his childhood classmate, Stephen Paddock, carried out the deadliest mass shooting in U.S. history. But he wasn’t surprised at all that someone from their hometown grew up to be violent.

“I can tell you how the bottle was loaded with gasoline,” said Palast, now a filmmaker. “But I don’t know what ignited it.”

Paddock isn’t even the first mass killer from their school, John H. Francis Polytechnic Senior High in Sun Valley, a struggling, sun-baked part of Los Angeles County’s San Fernando Valley. In 2008, Bruce Jeffrey Pardo, dressed in a Santa Claus suit and fired at fleeing party-goers at his in-laws’ house. He killed nine people before turning the gun on himself.

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“All too often, where you begin determines where you end,” said Palast, who spoke to TheWrap while standing outside the high school. “It’s a very fine line that divided my path from Paddock’s.”

He offered the obvious caveat that nothing justifies, forgives or explains what Paddock did.

Almost a month after Stephen Paddock opened fire on a crowd at a country music festival in Las Vegas, his former classmates are still trying to understand how a boy they remembered as withdrawn and quiet could have gone on to kill 58 people and wound hundreds more, before shooting himself. They described him as bright, but with no close friends anyone could recall.

“He was very much a loner,” another former classmate, film composer Michael O’Neill, told TheWrap. “He was kind of an enigma. He’d be sitting by himself at lunch.”

When police broke into the 32nd-story Mandalay Bay hotel room from which Paddock fired, they found handwritten calculations of distance and trajectory to the crowd below. One of the officers suggested to “60 Minutes” that Paddock “must have done the calculations online or something.”

But Palast doubts he needed help to do the math.

“He was a real brain, a math whiz,” Palast said. “I noticed him in Algebra, we were in the special high-track classes. He finished his math test before I did, and I was quick. I was like, wow… that kid!””

“He could have gone to Stanford or UCLA. But we didn’t go to Beverly Hills High,” Palast added. “We were on track to work at Lockheed Martin.” (Paddock worked for a predecessor of the aerospace company from 1985 to 1988, when it closed.)

His childhood wasn’t normal. He was 7 years old and living in Tucson in 1960, when F.B.I. agents showed up at the family’s home to arrest his father. Benjamin Hoskins Paddock was a bank robber the FBI once described as “psychotic.”

Stephen Paddock’s mother, Doroles, moved her four sons to Sun Valley soon after Benjamin’s Paddock’s arrest. He was sentenced to prison in 1961, but eventually escaped. Paddock’s brother has said their father played little role in their lives after their move to California.

Sun Valley is still a place for many people in transition. Today, the dusty street where Paddock grew up is littered with tents of those who have fallen on hard times. People live out of RVs parked throughout the neighborhood.

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“At the time it was the bottom of the bottom,” Palast said of their old neighborhood, still overshadowed by four imposing smokestacks from a nearby power plant.

“In the old days when they burned coal you couldn’t see the mountains, the sky was never blue and everything was covered with toxic coal dust. So you can imagine who would agree to live in houses like these,” Palast said.

Another former classmate, Richard Alarcon, who went on to become a California state senator, said he remembered Paddock from his Fernangeles Elementary School days, where the two would often played sports, including pickup football.

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“He wasn’t a sports superstar but he wouldn’t be the last one picked when we were picking teams either,” Alarcon said. “He was an average kid socially.”

Alarcon remembered a class competition where students were tasked with building a bridge made of balsa wood. Despite being instructed not use any glue, Paddock’s submission was “all white glue.”

“It seemed like he didn’t care that everyone knew he cheated,” Alarcon said. “We all just laughed it off.”

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John King, another former classmate from Richard E. Byrd Middle School as well as high school, said he remembered walking by Paddock’s home to and from junior high every day.

“He was the paperboy delivering the giveaway paper,” he said. “If I happened to be outside when he was delivering it, we’d sometimes chat.”

But King says Paddock made no strong impression on him.

“I wouldn’t call him a joiner,” he said.

Though classmates said Paddock wasn’t popular with girls, he did end up marrying a former classmate, one of two short-lived and childless unions.

“He never raised his hand at class,” Palast went on to say. “I was in his classes for 10 years, I don’t remember him saying a peep unless he was called on. He made himself as invisible as possible.”

After school, he used his math skills to invest in real estate, work for the IRS — and gamble.

“He took whatever money he had plus some money from family and brought crappy apartments in Downtown L.A. and that made some money,” Palast said. “But then he took his winnings and became a gambler.”

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King said that when he and Paddock both worked for the IRS in 1978, they would often meet for casual game nights.

“Once a month we’d have a nickel-dime-quarter poker game at somebody’s house,” King said. “Steve would join us every once in a while. I don’t remember him as an exceptionally aggressive card player.”

Paddock was reportedly gambling heavily in the weeks before he snapped. According to the Times, Paddock had developed a “methodical style” and skills that sometimes won him tens of thousands of dollars in one sitting.

The Las Vegas Metropolitan Police said they did not know Paddock’s name before the shooting and believe he acted alone. A clerk at Guns & Guitars, where Paddock purchased one of the rifles used during the attack, told NBC News that Paddock “never gave any indication or reason to believe he was unstable or unfit at any time.”

Scientists will soon examine Paddock’s brain for neurological diseases, according to the Times.

After the shooting, Paddock’s brother, Eric, said Stephen Paddock was “just a guy.” That’s also how he seemed to his old classmates.

“We were shocked,” King said. “You wouldn’t think that any human being would be capable of that. But he was a low-key person, which made it even more of a surprise.”