"Following an extensive investigation, the FBI and NCIS have determined that this attack was inspired by a foreign terrorist group, the final criteria required for the awarding of the Purple Heart to this sailor and these Marines," Mabus said in a statement. "This determination allows the Department of the Navy to move forward immediately with the award of the Purple Heart to the families of the five heroes who were victims of this terrorist attack, as well as to the surviving hero."
"We've investigated Chattanooga as a terror attack from the beginning," Director James Comey said, according to a report from Fox News. "The Chattanooga killer was inspired by a foreign terror organization. It's hard to entangle which particular source … there are lots of competing poisons out there."
Mabus said he hoped the award would comfort the families in some way.
"Although the Purple Heart can never possibly replace this brave sailor and these brave Marines, it is my hope that as their families and the entire Department of the Navy team continue to mourn their loss, these awards provide some small measure of solace," he said. "Their heroism and service to our nation will be remembered always."
The awarding of the Purple Heart raises questions about the possibility of valor awards for displays of heroism at the scene. Two service members, including two service members -- a Marine and the NOSC commanding officer -- who returned fire on the shooter, Muhammad Abdulazeez.
Marines who were at the scene told Military Times in August that the actions of Lt. Cmdr. Timothy White, who waylaid the shooter by firing his personal weapon, gave the Marines inside the NOSC a chance to get more people to safety, saving lives.
The subject of valor awards for troops' actions during terror attacks has come up repeatedly since the attacks on Sept. 11, 2001. The question came up again in wake of the foiled August attack on the French train, where Airman Spencer Stone's, Oregon National Guardsman Alek Skarlatos and a traveling companion stopped a lone gunman from carrying out an attack.
The Air Force ultimately awarded Stone the Airman's Medal, which is the highest non-combat valor award. Air Force Secretary Deborah James said in a September interview that the services were still coming to terms with the awards system in an era when the troops are being targeted far way from any traditional battlefield.
"This really is a worldwide threat situation," James said, adding that the entire military medals and awards system is "is being looked at right now within the Department of Defense. We're trying to think that through."
A Defense Department-wide review of the awards system has been conducted and the report is with Defense Secretary Ash Carter. The report was scheduled to be released this month, according to a Defense Department spokesman.
In a statement to Navy Times, Mabus spokesman Lt. Eric Durie said the secretary was waiting on the FBI determination to make a call on the Purple Heart.
"Part of the process in the case of Chattanooga is allowing the FBI's investigation to run its course. Once the FBI's detailed investigation is complete, and we have reviewed all applicable information, we will make our final award determination," Durie said.
David B. Larter was the naval warfare reporter for Defense News.