During a news conference on Wednesday, Ed Reinhold, the FBI's special agent in charge in Knoxville, said investigators are still looking into whether Chattanooga gunman Muhammad Youssef Abdulazeez had been radicalized.
Reinhold said the FBI believes Abdulazeez acted alone, without the assistance of anyone else when he attacked two military sites in Tennessee last week.
Abdulazeez killed Gunnery Sgt. Thomas Sullivan, Staff Sgt. David Wyatt, Sgt. Carson Holmquist and Lance Cpl. Squire Wells, all of the Marines; and Randall Smith, a Navy petty officer 2nd class.