Police on Friday arrested a 24-year-old woman in connection with the gunman who ambushed and killed two firefighters as they battled a blaze in upstate New York, police said.

Dawn Nguyen of Rochester, New York, faces charges of filing a falsified business record, which is thought to be linked to the purchase of the AR-15 rifle and 12-gauge shotgun that the gunman had with him during the attack. The nature of her alleged relationship to the shooter -- identified by authorities as William Spengler, 62 -- is unclear.

Nguyen was "turned her 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," said state police Investigator James Newell.

The shooter -- who was 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.

Nguyen's attorney was not immediately available for comment.