State Attorney General Joseph Foster said Monday night that Brentwood Police Officer Stephen Arkell, 48, answered the domestic dispute call at about 4 p.m. and was fatally shot when he arrived at the house.
About an hour after the shooting, the house burst into flames and video showed flames eating through the roof of the modern yellow building. Firefighters were kept away from the scene and soon a massive explosion blew the front off the house. Within an hour, it was leveled.
Nolan is the son of the homeowner, 86-year-old Walter Nolan.
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.
"Like so many of our first responders do on a daily basis, Officer Arkell courageously put his life on the line to protect others, and in doing so, was tragically taken far too soon," she said.
Debra Vasapolli, director of public relations at Exeter Hospital, said one person was taken to the hospital but said that person was not the victim of a gunshot wound. She declined to provide more details or say if the victim was the elder Nolan.
Neighbor Wayne Hughes told the Portsmouth Herald that police responded to the house after neighbors heard an argument Monday afternoon and called 911. His wife, Susan, said she saw a police officer arrive at the home and then heard "rapid gunfire."
She said she saw Walter Nolan being taken from the scene by ambulance before she was evacuated from the area.
Aerial coverage from WMUR-TV showed flames burning through the roof of the house and an explosion punching out the front of the house shortly after 5:30 p.m. Within minutes of the explosion, the house was engulfed in flames as black smoke billowed over the neighborhood.
Firefighters started attacking the blaze around 6 p.m. It was largely out about a half-hour later and didn't appear to have spread to neighboring houses.