Authorities say a 24-year-old woman has been charged in connection with the guns used in the killing of two firefighters responding to a house fire in Webster, N.Y. on Christmas Eve.

Authorities announced Friday that Dawn Nguyen, of Greece, N.Y., has been charged with knowingly making a false statement in connection with the purchase of a Bushmaster semiautomatic rifle and a 12-gauge shotgun that William Spengler had with him after setting his house ablaze and shooting at responding emergency crews.

Nguyen, police say, used to live next door to Spengler. The firearms were purchased by Nguyen in Henrietta, N.Y. in 2010 and acquired on behalf of Spengler, police allege.

As an ex-convict, 62-year-old Spengler wasn’t allowed to possess weapons. He had served 17 years in prison for manslaughter after killing his grandmother with a hammer in 1980.

“It is absolutely against federal law to provide any materially false information relating to the acquisition of firearms,” U.S. attorney William Hochul said at a Friday press conference.

In addition to federal charges, New York State police arrested Nguyen on one count of falsifying business records for allegedly purchasing guns for Spengler.

Spengler had enough ammunition for three weapons including a military-style assault rifle when he lured firefighters to the upstate New York neighbourhood by setting his house on fire.

When firefighters arrived, Spengler shot at them, killing police Lt. Michael Chiapperini, 43, who also worked for the fire department, and firefighter Tomasz Kaczowka, 19. Three other people were wounded, including two firefighters who were struck by bullets. They are recovering.

Spengler then killed himself as houses burned. Authorities found his body on a nearby beach hours after the attack.

Hochul said authorities are continuing the investigation.

“While William Spengler may have escaped the criminal justice system, those who provided the firearms to Spengler that he used on Christmas Eve to murder and wound the firefighters and the police officer will not escape the criminal justice system, “ Hochul said.

Investigators said earlier in the week Spengler had been “equipped to go to war, kill innocent people when he burned down his neighbourhood just before dawn on Christmas Eve.”

A typed-out note he left behind described his desire to “do what I like doing best, killing people,” police said.

On Tuesday, investigators sifting through the home found a body believed to be that of Spengler’s missing sister, 67-year-old Cheryl Spengler, who he was said to be living with.

Residents of the neighbourhood who had been evacuated were allowed to return Tuesday.