Julian Conley, 19, was transported to the Fulton County Jail after a felony murder warrant was issued for his arrest Tuesday, Atlanta police said in a statement. He also faces a charge of aggravated assault.
The girl, Secoriea Turner, was shot to death while riding in a car with her mother and a friend on July 4. The driver tried to pull into a parking lot that was barricaded after Brooks was killed on June 12.
The area was the site of racial justice rallies after Brooks, who was Black, was shot to death by Officer Garrett Rolfe, who is white.
Rolfe, who has been fired, has been charged with felony murder, aggravated assault with a deadly weapon and other counts after he shot Brooks twice in the back.
A second officer, Devin Brosnan, was charged with aggravated assault and violation of oath.
The parking lot where Secoriea was shot is a half-mile from the Wendy's. She was pronounced dead at a hospital.
Conley turned himself in after authorities released a photo of him over the weekend carrying a gun. The police department identified him as a person of interest in Secoriea's killing.
Speaking with reporters Wednesday, Conley's attorney, Jackie Patterson, said his client was arrested "solely because he refused to cooperate" with authorities.
"Once I identified him as the person in that picture and said we wouldn't cooperate, then they decided — let's show him, let's issue a felony murder warrant," he said.
Patterson had told NBC affiliate WXIA earlier that Conley saw four gunmen fire on Secoriea's car but that he didn't fire his weapon and couldn't identify who did.
Patterson said Wednesday that Conley was armed that day because he has a constitutional right to carry a weapon in public.