New York (CNN) -- The gunman who ambushed and killed two unsuspecting firefighters as they battled a blaze in upstate New York couldn't buy his weapons legally so he allegedly got his neighbor's daughter to purchase them for him, said U.S. Attorney William Hochul.
Dawn Nguyen of Rochester, New York, faces charges over allegedly lying when she purchased an AR-15 rifle -- a .223-caliber weapon -- and 12-gauge shotgun that the gunman had with him during the attack.
Authorities say she told the gun dealer that she planned to be the owner of the weapons, but had instead purchased them on June 7, 2010,for gunman William Spengler.
"It is absolutely against federal law to lie relating to the acquisition of firearms," said Hochul, who said Spengler indicated in a suicide note that he had gotten the weapons from the neighbor.
Nguyen, 24, was "turned ... over to ATF (Bureau of Alcohol, Tobacco, Firearms and Explosives) agents to be processed at the federal level, and arraigned by a federal magistrate this afternoon," according to state police Investigator James Newell.
Spengler, 62 -- who had been convicted of killing his grandmother decades ago -- used the same type of weapon employed in the recent assault on Sandy Hook Elementary School, which left 26 people dead, including 20 children. As a convicted felon, Spengler was not allowed to legally possess weapons.
"He was equipped to go to war," Webster Police Chief Gerald Pickering said. The gunman was found dead of a self-inflicted gunshot wound hours later.
In his possession were three firearms, including two .223-caliber Bushmaster rifles and a Mossberg 12-gauge shotgun. While Nguyen's charges involve two weapons, authorities indicated the possibility of additional charges regarding the third weapon.
Nguyen's attorney was not immediately available for comment. If convicted, she could face up to 10 years in jail and $250,000 fine.
CNN's Kristina Sgueglia and Laura Ly contributed to this report.