What Georgia law says
Georgia law allows a person to use deadly force "only if he or she reasonably believes that such force is necessary to prevent death or great bodily injury to himself or herself or a third person."
In addition, the Atlanta Police policy manual, which was most recently updated last week, says that an officer can use deadly force when "He or she reasonably believes that the suspect possesses a deadly weapon or any object, device, or instrument which, when used offensively against a person is likely to or actually does result in serious bodily injury and when he or she reasonably believes that the suspect poses an immediate threat of serious bodily injury to the officer or others."