(CNN) For years, Marcus Braziel took his customers at their word when they showed up with wads of cash to buy one of the customized AR-15-style rifles he advertised for sale on the internet.
If they said there was no legal reason to prevent them from owning a gun, Braziel said, that was good enough for him. He saw no need for obtaining a license and conducting formal criminal background checks.
But that was before federal agents showed up at his door in Lubbock, Texas, and told him they'd traced one of his weapons to a mass shooter.
"I wanted to vomit," Braziel recalled in an exclusive interview with CNN. "My life has not been the same since. I will be forever sorry."
Braziel, 45, pleaded guilty Wednesday in US District Court in Lubbock to felony charges of dealing and manufacturing firearms without a license and filing a false tax return that failed to report income from his gun sales. He faces up to five years in federal prison under a plea deal with prosecutors.
Among the firearms he illegally sold was an AR-15-style weapon that Seth Ator used to kill seven people and wound 25 others in a shooting spree in the Midland-Odessa area of Texas last year.
Braziel said his brief encounter with Ator and its horrific and lingering consequences have made him a fervent believer in universal background checks on would-be gun buyers.
"I feel responsible for the role I played in selling him a firearm," he told CNN. "My primary objective is that this never happen to anyone else."
Erin Nealy Cox, the US Attorney for the Northern District of Texas, said the case against Braziel underscores that dealing firearms without a license "isn't some obscure, meaningless, technical violation."
"It is unlawful conduct that has real world impact and the potential for devastating results," she said in a prepared statement. "The Justice Department is committed to enforcing our nation's long-held gun laws, designed to prevent firearms from falling into the wrong hands."
A 2019 CNN investigation found that unlicensed gun dealers like Braziel provided a steady flow of weapons to people who are either barred from owning guns or want guns that can't be traced back to them. Such weapons have often turned up in the hands of convicted felons, at crime scenes, and in police investigations, including cases of armed robbery and murder.
At the heart of the problem is a vaguely worded federal statute that has frustrated efforts by law enforcement to combat the problem of illegal gun dealing, and effectively helps sustain a marketplace for black market gun sales. The law is fuzzy on the distinction between a casual seller of firearms who is not required to conduct background checks on prospective buyers and a licensed gun dealer, who is.
Braziel told CNN that he saw himself as a firearms hobbyist in 2016 when Ator showed up at his home with $750 to buy the rifle he would later use in the attack.
He said he had no inkling that Ator was prohibited from possessing a weapon due to a past involuntary stay in a mental institution.
"There was nothing about him that made me believe he was unstable," Braziel said. "He was very calm, collected. He looked completely ordinary to me."
He said that Ator either did not yet have — or that he did not notice — a tear drop tattoo on his left cheek that is visible in an undated photo released by authorities after the attack. A plaintiff's attorney who earlier this year filed a civil lawsuit against Braziel on behalf of some of the victims' families told reporters the markings should have been a red flag prompting closer scrutiny.
As with all of his customers, Braziel said, he had Ator sign a bill of sale that contains language stating that the buyer is not banned from owning a weapon. Ator used his middle name as his last and listed a P.O. box for an address.
"I had no reason to not believe him," Braziel recalled.
Because he was not a licensed dealer, Braziel said, he had no means — and in his mind at the time, no responsibility — to conduct a background check, and did not do so.
It would be three years before the sale came back to haunt him in the aftermath of last year's attack.
The incident began when Ator, 36, opened fire on Texas troopers who pulled him over for failing to signal.
He then led police on a chase, firing shots at random people and at one point carjacking a US postal truck. Those fatally shot were between 15 and 57 years old, authorities said. Among the wounded were a 17-month-old girl and three law enforcement officers. Ator was killed in a shootout with police in a movie theater parking lot.
Shortly after the attack, agents with the Bureau of Alcohol, Tobacco, Firearms and Explosives arrived at Braziel's home, asking questions about guns he'd sold.
He said they'd been there about 15 minutes when they revealed that one of the guns had been used by Ator.
He said both he and his wife were devastated when they heard that, and that the victims and their families have remained in their thoughts ever since.
"I cannot begin to understand how they feel," Braziel said, his voice filled with emotion.
In the year since, agents and prosecutors have been slowly building a case against Braziel, who works as a respiratory therapist, for being an unlicensed gun dealer.
The federal statute governing gun dealers says anyone "engaged in the business" of selling firearms requires a license. "Engaged in the business" means devoting "time, attention and labor to dealing in firearms as a regular course of trade or business with the principal objective of livelihood and profit through the repetitive purchase and resale of firearms."
The law states that it does not apply to someone engaged in only occasional gun sales or collectors or hobbyists adding to, or selling from, their personal collection.
To the frustration of gun and gun control advocates alike, the law places no set number of transactions that differentiates between a person engaged in the business and one who makes "occasional sales."
In court documents filed Wednesday, Braziel admitted to dealing and manufacturing firearms without a license from 2014 to 2018. He advertised gun sales on the internet and conducted transactions — almost always for cash — in his garage or in the parking lot of a local sporting goods store, according to a plea agreement and related documents filed by Assistant US Attorney Jeffrey R. Haag.
Braziel custom built many of the weapons he sold, beginning with a key gun component known as a lower receiver, which ATF considers a firearm in and of itself.
Braziel would buy the lower receiver, a hollow mass of metal or plastic surrounding the trigger area of a gun, and attach other parts to make it a fully functioning weapon. He would also employ a technique called "hydro-dipping" to give the body of a weapon a unique artistic appearance.
Braziel told ATF agents that he and a family member would "buy them, build them, play with them, and then sell them when they were finished," court records state. Though Braziel said he considered this a hobby at the time, agents later discovered items about gunsmithing and starting a business on his laptop computer in January 2015.
According to prosecutors, Braziel sold firearms to three other people barred from possessing weapons, in addition to Ator. Braziel also failed to declare $3,800 from the sale of firearms on his 2016 tax return, according to court filings. Agents seized 29 firearms from Braziel's house when they executed a search warrant in the days after the shooting.
His lawyer, Daniel W. Hurley, said Braziel read an ATF pamphlet called "Do I Need A License to Buy and Sell Firearms?" several years ago and concluded at the time that he did not. He has since acknowledged having willfully violated the law, Hurley said.
But the lawyer said agreeing to plead guilty was not an easy decision.
Hurley said he presented the case to a mock jury earlier this year and that "a clear majority thought Marcus was not guilty."
Braziel was motivated to take the plea nonetheless, Hurley said, because of the threat of a lengthy prison sentence if he lost at trial and because he wanted to speak out about the dangers of dealing guns without a license.
"It's too risky. People can die because of it," Hurley said. "Marcus wants the whole world to know that."