Updated

A woman has pleaded guilty to three federal charges related to her purchase of firearms used by a felon to kill two upstate New York firefighters on Christmas Eve 2012.

Dawn Nguyen (wehn) of suburban Greece, outside Rochester, has already been sentenced to up to four years in prison on related state charges of falsifying business records.

Local media report that Nguyen pleaded guilty Thursday in federal court. She will be sentenced Aug. 28.

Nguyen bought a semi-automatic rifle and a 12-gauge shotgun in 2010 for neighbor William Spengler Jr., a felon who was prohibited from owning weapons.

Spengler set fire to his home on Lake Ontario in Webster in the pre-dawn hours of Dec. 24, 2012, and lay in ambush until firefighters arrived. He shot four firefighters before committing suicide.