Police in western New York state have arrested and charged a 24-year-old woman in connection with the guns used Monday to ambush and kill two firefighters who had responded to a house fire.

Authorities say Dawn Nguyen of Rochester faces charges of falsifying documents, but no details were immediately available. Federal charges against her are also pending.

Shooter William Spengler is believed to have used the AR-15 semi-automatic rifle and shotgun to kill the firefighters and wound two others.

The Bushmaster assault rifle found at the scene of the ambush is similar to the one used by the gunman who massacred 20 school children and six adults in Newtown, Connecticut earlier in the month.

Authorities have been probing how Spengler, who died at the scene of the ambush from a self-inflicted gunshot, acquired the weapons. Having spent 17 years in prison for killing his grandmother, Spengler was not allowed under federal law to own weapons.

Nguyen's lawyer said she purchased the weapons legally, and that they were stolen.