The death of Navy Petty Officer 2nd Class Randall Smith, a reservist serving on active duty in Chattanooga, was announced by the Navy.
Muhammad Youssef Abdulazeez opened fire on two military facilities in the city on Thursday and killed four US marines, before being killed himself by police.
The other four victims were identified as Gunnery Sgt Thomas J Sullivan, of Hampden, Massachusetts; Staff Sgt David A Wyatt, of Burke, North Carolina; Sgt Carson A Holmquist, of Polk, Wisconsin; and Lance Cpl Squire K “Skip” Wells, of Cobb County, Georgia.
Abdulazeez sprayed dozens of bullets at a military recruiting centre in Chattanooga, then drove to a Navy-Marine training centre a few miles away and shot at the installation
Prosecutors in eastern Tennessee said the attacks by the 24-year-old, born in Kuwait, are being treated as a terrorism investigation.
Abdulazeez did not appear to have been on the radar of federal authorities before the bloodshed, but counter-terrorism investigators are taking a deep look at his online activities and searching for clues to his political views.
Residents in the quiet neighbourhood in Hixson, Tennessee, where Abdulazeez lived in a two-storey home, said they would see him walking along the wide streets or doing yard work. One neighbour recalled Abdulazeez giving him a ride home when he was stranded in a snowstorm.
“It’s kind of a general consensus from people that interacted with him that he was just your average citizen there in the neighbourhood. There was no reason to suspect anything otherwise,” said Ken Smith, a city council official.
Abdulazeez graduated from Red Bank High School in Chattanooga, where he was on the wrestling team.
He got an engineering degree from the University of Tennessee at Chattanooga in 2012 and worked as an intern a few years ago at the Tennessee Valley Authority, the federally owned utility that operates power plants and dams across the South.
For the last three months, he had been working at Superior Essex, which designs and makes wire and cable products.
In April, he was arrested on a drink-driving charge, and a mugshot showed him with a bushy beard.
A federal law enforcement official said authorities were searching Abdulazeez’s computer but had not found an extensive online presence and had not uncovered any evidence he was directly influenced by Islamic State.