Micah Ward, the GBI special agent in charge in Statesboro, said Thursday that the state investigators had been summoned by Tybee Police Chief James Price.
"The scope of our investigation is simply to look into whether or not there were any illegal acts committed on the part of the police officers," Ward said. "Once we've finished, we'll put together a case file and provide it to the district attorney."
On Friday night, Clifford Grevemberg, 18, was wrestled to the ground and Tased by Tybee officers Timothy Sullivan and Travis Daniel, who suspected the teen was intoxicated, according to incident reports.
Grevemberg, who had been sitting on a curb outside the Rock House bar, suffered a broken front tooth and scrapes on his face and knee. He was released that night on a disorderly conduct charge.
Grevemberg, who also suffers from a heart condition, has never consumed alcohol, family members said.
On Thursday, Price said the GBI had been requested to "perform a thorough and objective investigation into the incident, using whatever means are available or discoverable."
Price added: "The investigation was begun today, May 27, with interviews of the two officers directly involved, a review of the reports filed on the incident and a review of the department's Use of Force Policy with an emphasis on our Taser policy."
Dario Mariani, Grevemberg's brother, welcomed news of the external probe.
"I think it's good - they need to be investigated," he said. "I'm sure that (police) are doing that to cover their own tail, but regardless it needs to happen. They need to get to the root of the problem and eliminate the problem."
Ward said agents would interview everyone involved in the incident, including witnesses.
"We're going to be very methodical and make sure we cover every aspect," Ward said. "We're not going to get in a hurry."