( CNN ) -- The man believed to have killed a police officer Monday before an explosion rocked the New Hampshire duplex where the shooting happened did not have a criminal record -- not even a motor vehicle record -- prosecutors said Tuesday . Investigators believe that Michael Nolan , 47 , shot and killed police officer Steve Arkell before losing his own life in a fire and explosion that followed . The Brentwood , New Hampshire , Police Department was in mourning Tuesday , even as investigators tried to understand how one officer 's response to a domestic disturbance call ended this way . Monday was the first time that police were called to the home shared by Michael Nolan and his father Walter Nolan , 86 , said Jane Young , chief of the New Hampshire attorney general 's criminal bureau . Young said officer Arkell responded to a call at the home Monday afternoon , where the younger Nolan was allegedly swearing at his father . When Arkell arrived , he met with Walter Nolan in front of the house and was granted permission to enter , Young said . After the officer entered , three volleys of gunfire were heard , and another emergency call was made by a neighbor to report the shots , Young said . A second officer arrived and entered the residence , where `` he noticed that there was a wall that had been sprayed with bullets , and he saw officer Arkell on the floor , on his back , '' Young said . The officer was met with gunfire and he retreated to call for backup . As authorities built up a presence around the house , a fire was spotted by the front , followed by an explosion that was captured live on air by CNN affiliate WCVB-TV . A witness told police that arguing had been heard from the Nolan home before , but police had not been called . Young said investigators may never know what prompted the argument because of the father 's diminished mental state and difficulty communicating . The incident is being investigated by the state and federal authorities , according to Foster . The 48-year-old Arkell was married and the father of two teenage girls , affiliate WMUR reported . New Hampshire Gov . Maggie Hassan ordered that flags in the state be flown at half-staff in honor of Arkell . `` I join all Granite Staters in mourning the loss of Brentwood police officer Steve Arkell , who died ... doing his job , protecting his community , '' she said . Brentwood is a town of about 4,200 , located 50 miles north of Boston . CNN 's Ed Payne , Janet DiGiacomo and Susan Candiotti contributed to this report .
Prosecutors believe Michael Nolan shot and killed a police officer . Nolan himself is believed to have died in an ensuing fire and explosion . There is no criminal record for Nolan -- not even a motor vehicle record .