The federal investigators used the name and address to track down Haig.
He was charged shortly before holding a news conference Friday. Haig did not have a license to manufacture or sell armor-piercing ammunition, according to authorities.
Haig made an initial court appearance before a federal magistrate in Phoenix and was freed under conditional release pending a February 15 status conference set for the case, prosecutors said.
If convicted, Haig could face up to five years in prison and a $250,000 fine. "He told me exactly what he wanted". Haig advertised armor-piercing incendiary ammunition on his website, which now says the business is "closed indefinitely".
Haig held Friday's news conference to protect his reputation, he and his attorney said. He also said none of the ammunition recovered at Las Vegas crime scenes would have tool marks on them consistent with his reloading equipment.
It also alleges that Federal Bureau of Investigation agents searching Haig's home on October 19 found armor-piercing ammunition.
This is a breaking news story.
Arizona ammunition Douglas Haig, 55, was charged with manufacturing illegal armor-piercing bullets on Friday after police discovered he sold 720 to Stephen Paddock, the shooter from the Las Vegas Route 91 Harvest Festival mass shooting.
"You would have seen red streaks coming from the window", Haig said.
The complaint states that Haig spoke to Paddock on September 19 and provided him directions to his Mesa, Arizona, residence, where the sale was later completed. "I gathered it up, put it in a box, told him what he owed me. I handed him a box with the ammunition in it, and he paid me and he left". "At no time did I see anything suspicious or odd or any kind of tell, anything that would set off an alarm".
Fifty-eight people were killed and hundreds injured in the shooting. Haig's identity emerged by mistake after his name was not redacted in court documents.
The only other person of interest named in search warrants was Paddock's girlfriend, Marilou Danley.
Lombardo sought to dispel conspiracy theories linked to multiple gunmen or ties to Islamic State and took the unusual step of releasing his agency's preliminary investigative report.
Haig said he is cooperating with investigators.
Haig defended himself as merely a vendor, saying, "I had no contribution to what Paddock did".
He said he was 'horrified that this man would do something like that, ' and called the news 'probably one of the most frightful things I've ever been told or heard of'.
Haig has since shut down has ammunition business. In it he explained how he first met Paddock at a Phoenix gun show and calmly recounted having three separate phone conversations with Paddock whom he described as "very well dressed, very well groomed, very polite, very respectful". Haig could not recall the exact wording. Haig was at work, so the Arizona man asked Paddock to call him later.
He did not have the quantity of tracer ammunition on hand that Paddock was seeking, so Paddock contacted him several days later and lined up a sale at Mr Haig's home.
Haig added that he typically sold ammunition to customers at gun shows or shipped out the product.