The suspect’s father told US media the soldier sent a cryptic text message to a family member on the morning of the shooting.
Eddie Radford told the New York Times that his son sent a message to his aunt saying “that he loved everybody, and that he will be in a better place because he was about to do something”.
Mr Radford, who did not see the text message himself, said he had not noticed anything unusual about his son’s behaviour prior to the shooting. “It’s hard for me to process,” he added.
He also told the New York Times his son had sought a transfer from Fort Stewart and had complained about alleged racism on the base. Asked about that claim, the Department of Defense said it would not comment on an ongoing investigation.
On Thursday, six soldiers were honoured with a service medal for their role in stopping the gunman.
“Under duress and fire, they ran into battle to the sound of the gunfire, took down the assailant, and then took care of their comrades, and that made all the difference,” said US Army Secretary Dan Driscoll.
“The heroism shown under fire is something that we should all aspire to know.”
The gunman opened fire at around 11:00 local time on Wednesday at a sprawling military base located around 240 miles (386km) south-east of the state’s capital, Atlanta.
Soldiers ran to subdue the gunman and wrestled his gun away, Gen Lubas said, who described how one, a non-commissioned officer, jumped on top of the suspect and restrained him before police arrived.
Four other soldiers provided medical care to the victims “with no hesitation” and helped stop the bleeding before paramedics arrived on the scene.