State Attorney General Joseph Foster said Brentwood police Officer Stephen Arkell, 48, answered the domestic dispute call at about 4 p.m. Monday and was fatally shot when he arrived. A second officer tried to enter but was driven away by gunfire.
About an hour after the shooting, the house burst into flames. As flames burned through the roof of the building, firefighters were kept away. Then suddenly, an explosion blew the front off the house.
Suspected gunman Michael Nolan, 47, was presumed dead in the fire that demolished the home. Nolan was the son of the homeowner, 86-year-old Walter Nolan.
Investigators believe the dispute was between the father and son. A neighbor says she saw Walter Nolan being taken from the scene by ambulance before she was evacuated from the area.
Arkell, who was married and had two teenage daughters, had worked for the Brentwood Police Department for about 15 years as a part-time officer. Gov. Maggie Hassan directed that flags fly at half-staff in honor of Arkell.
"The entire state of New Hampshire is in mourning over the tragic loss of Brentwood Officer Steve Arkell," she said in a statement. "Officer Arkell bravely answered the call of duty and made the ultimate sacrifice, a heroic demonstration of his commitment to the safety of his fellow citizens.
The Associated Press contributed to this report.
