Jacob Christian Muse, 21, of College Park, was charged with three counts of malice murder, the Georgia Bureau of Investigation said.
Details of what led investigators to the arrest of Muse were not immediately available.
Tommy and Evelyn Hawk and their grandson Luke were found the night of April 8 at the Lock, Stock & Barrel, which is owned by the family.
The Hawk family did not have a comment immediately following the arrest.
Muse was booked into the Coweta County jail.
Officials said the joint investigation into the murders remains open and very active.
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Who were the victims of the Granville gun range shooting?
Tommy and Evelyn Hawk and their grandson Luke. (Provided photo)
Grantville Police Chief Steve Whitlock said Tommy Hawk, the owner of Lock, Stock & Barrel, died in the shooting as well as his wife Evelyn and their grandson Luke.
Luke is the son of Coweta County coroner Richard Hawk, who was one of the first at the scene on Friday night. Tommy Hawk and Evelyn Hawk were Richard Hawk's parents.
When, where was the gun range shooting?
The shooting happened sometime on the night of April 8 after the business closed.
Lock, Stock & Barrel is located at 514 Bohannon Road in Grantville.
Initially the investigators said the robbery happened between 5:30 p.m. and 6 p.m.
Grantville police said officers were dispatched to the scene shortly after 8 p.m.
What was stolen from the Grantville gun range?
The Bureau of Alcohol, Tobacco, Firearms and Explosives said an unknown number of guns were missing, but Grantville police estimated about 40 guns were missing.
Police also said someone took a camera DVR from the business.
What agencies are assisting in the Grantville gun range shooting investigation?
It's the Grantville Police Department's case, but the small department employs about 13 officers, the chief said Monday.
The Georgia Bureau of Investigation and ATF are assisting.
Whitlock also said the Coweta County Sheriff's Office and the Troup County Sheriff's Office are also providing some support.
Reward in Grantville gun range shooting investigation
There was a combined reward of $25,000 for information leading to an arrest and conviction in the investigation.
ATF, the City of Grantville, Georgia and the National Shooting Sports Foundation, the trade association for the firearms industry, announced a combined reward of up to $15,000.
Gov. Brian Kemp issued an executive order to add $10,000 to the reward, increasing it to a total of $25,000.
It was not immediately known if anyone will be claiming the reward money.