In the first full account of the attack, the FBI said Mohammad Youssef Abdulazeez hunted for victims.
Investigators are trying to determine if one of the Marines returned fire and possibly wounded Abdulazeez.
In the wake of Thursday’s attack, investigators sought a motive and security was heightened at military recruiting posts around the United States.
Although U.S. officials said Mohammad Youssef Abdulazeez’s foreign trips — including to Jordan, where he had family ties — did not raise suspicions, investigators are looking into whether he might have been radicalized overseas.
Mohammad Youssef Abdulazeez blogged days before about living in a “prison” of monotony and praised early practitioners of jihad.
The suspect, identified as Mohammad Youssef Abdulazeez, was also killed during what is being called “an act of domestic terrorism” at a naval facility and armed services recruiting center.
Four Marines were killed at a pair of military facilities in Chattanooga before the gunman was killed.
The Iraqi, Umm Sayyaf, allegedly was involved in holding Kayla Mueller hostage in militant territory.
The 23-year-old, a felon, was charged with illegal possession of firearms, authorities said.
Military prosecutors earlier this year learned about a large cache of images of the agency’s prisons.