LOS ANGELES (CNN/KCAL/KCBS) - An undercover investigation into an assault-style weapons factory found that felons were able to build their own untraceable weapons and parts without undergoing any background checks.
Then federal prosecutors dropped the case.
For more than a year, investigators with the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) captured undercover video of Joseph Roh's shop.
The video showed that anyone off the street could walk into Roh's shop and make a gun, including more than two dozen people banned from owning one.
Roh appears on camera, confirming to agents what they knew was about to happen.
"Are you here to do, to make yourself a rifle right now? Is that what you're here to do?" Roh says.
"Yeah," the agent responds.
Roh helped customers assemble AR-15s at the unlicensed do-it-yourself assault-style weapons factory for about $1,000 per gun or they could make their own by pushing a button on his machine.
Investigators say Roh never performed background checks.
Agents with ATF warned Roh that he was breaking the law, but he continued to operate.
Agents raided the shop and he was indicted. If he had been convicted, he may have served a prison sentence.
In a strange legal turn of events, the judge wrote a tentative ruling, suggesting Roh was right all along: He didn't need a license to manufacture a key component of an AR-15.
It came down to what does and does not constitute the manufacturing of a firearm and whether a part on an AR-15 in the lower receiver is legally regulated. The ATF had long considered this part a firearm, but the judge didn't agree.
Adam Winkler, a UCLA Law professor, said this could jeopardize future prosecutions.
"This ruling could make it so that anyone could manufacture and sell these key component parts of an AR-15 to anyone without a serial number and without a background check," Winkler said. "It could lead to an explosion in the number of AR-15s out on the streets."
To prevent the judge's opinion from becoming law, the government cut a deal: Even though Roh admitted to illegally selling assembled AR-15s, he could go free and the entire case would go away if he shut down his business and obeyed the law for a year.
"The ATF had been proceeding in a way that in itself was illegal. The agency was arbitrarily rewriting the rules," said Gregory Nicolaysen, Roh's defense attorney.
Federal prosecutors said the intent of the law was to keep "firearms out of the hands of those not legally entitled to possess them" and that ATF's interpretation supported that.
Nicolaysen took the government deal, but considers his client a victim whose own customers included police officers and law-abiding citizens who just liked making guns.
"But again, there were customers he didn't know that bought parts, who made guns, who had no background checks," said Drew Griffin, a reporter with CNN.
"And that is true too," Nicolaysen replied.
Among Roh's clients were 19 convicted felons, six domestic abusers and someone who even admitted to trafficking guns into Mexico.
There was one more dangerous customer of Roh's business.
On June 7, 2013, a mass shooting happened in Santa Monica, California.
A 23-year-old, who had once been hospitalized for mental health and later prohibited from buying a gun, used an AR-15 to kill five people before being shot and killed by police.
A receipt shows that five months before the shooting, the killer purchased a major part of an AR-15 from Roh’s shop.
Though Roh's attorney said it was never substantiated, ATF agents believe the killer used that part to build the gun used in the shooting.
"There has to be accountability," said Margaret Quiñones-Perez, who lost her niece and brother-in-law in the shooting.
She doesn't accept Roh's defense that he was only selling parts of a gun.
"You can call it a business, you can call it a parts company, you can call it whatever it is, but I can look at the man in the face and say, 'You were part of a killing,'" she said. "I don't care what percentage it was - you facilitated the killing of my family."
Barring any further run-ins with the law, in June of next year Row's record will be wiped clean, and the case itself will legally disappear.
This case is another example of how the ATF is stymied by vague federal gun laws and the inability to get any of them changed.