THE man who made armour-piercing ammunition without a license and sold it to the Las Vegas gunman who committed America’s worst mass shooting has been charged.

Stephen Paddock, 64, killed himself after he carried out a rampage from the 32nd floor of his hotel suite on Las Vegas’ famed Strip on October 1, which left 58 people dead at the Route 91 Harvest music festival. Another 422 people were injured as a result of Paddock’s gunfire.

Now Douglas Haig, 55, from Arizona has been formally charged with making the illegal ammunition.

He was previously a person of interest. Haig has since held a news conference to say he was innocent and had only briefly met Paddock who bought 720 rounds of ammunition from him once.

Haig told reporters he has received death threats in the days since his name was accidentally released in police warrants made public by a Nevada judge.

Haig also said he sold ammunition as a hobby for nearly 20 years while working full time as an aerospace engineer.

“I had no contribution to what Paddock did,” he said.

“I had no way to see into his mind. The product that I sold him had absolutely nothing to do with what he did. I’m a vendor. I’m a merchant whose name was released.”

Haig said he met Paddock briefly at a gun show in Phoenix, about a month before the shooting.

Paddock then allegedly came to Haig’s home in Mesa, on the outskirts of Phoenix, in September last year to buy some ammunition.

Haig had previously operated ‘Specialised Military Ammunition,’ an internet business selling armour-piercing bullets, some of them highly explosive, according to a statement from US Attorney Dayle Elieson of Nevada.

Records show he had done business in Nevada, Texas, Virginia, Wyoming and South Carolina despite having no license to manufacture armour-piercing ammunition.

Haig told investigators he reloads ammunition but does not offer reloaded cartridges for sale, and none of the rounds recovered in Las Vegas crime scenes would have tool marks consistent with his reloading equipment.

But Elieson said forensic examiners had recovered reloaded, unfired .308 caliber cartridges in the shooter’s hotel rooms bearing Haig’s fingerprints.

Armour-piercing ammunition recovered inside the shooter’s rooms had tool marks consistent with Haig’s reloading equipment, the statement added.

The fingerprints were a vital clue that police needed to charge Haig.

Paddock asked for a box to carry the rounds to his car and Haig gave him a used box that included his name and address. He says that was their only transaction.

The name and address on the box is what led investigators to Haig.

Police believe Paddock, a wealthy retired accountant and compulsive video poker player who took Valium for anxiety, had lost a significant amount of money before his killing spree.

Technicians scouring Paddock’s computer found searches for firearms and elite police response teams, as well as “numerous photos of child pornography,” Clark County Sheriff Joe Lombardo said last month.

Paddock had stockpiled an arsenal of firearms in his room at the Mandalay Bay hotel before he rained fire down on a country music festival where about 22,000 people had gathered.

Haig has been charged with one count of conspiracy to manufacture and sell armour-piercing ammunition and was released on bail pending a preliminary hearing on February 15 in Phoenix.

He faces the maximum penalty of five years in prison, and possibly a $US250,000 fine ($A315,000), if convicted.

Haig’s lawyer repeatedly said at the press conference that his client had nothing to hide and that “the reason he opts to speak to the press today is basically to protect his reputation”.

Police are still yet to determine the motive for Paddock’s shooting rampage, and the investigation continues.