Authorities said early Saturday that Darrell Ingram was arrested and charged with two counts of murder and one count of aggravated assault.
Stacy Smalls, 19, died from gunshot wounds at a Savannah hospital shortly after the shootings. Officials said Smalls was not a student.
Ramone Kimble, a 16-year-old student at Savannah High School who was shot in the head, died shortly after 11 a.m. Saturday at Memorial Health University Medical Center in Savannah, nursing supervisor Ellen Pinckney said.
Lamar Jenkins, a 16-year-old Beach High School student, was shot in the buttocks. He was treated and released from the hospital.
Ingram is not a student at the high school, and neither is the victim who died, police said. Beach High School officials said all three victims were students in the district, although it was unclear what schools they attended.
The shootings took place near Beach High School where a dance was held to celebrate the Lady Bulldogs' state championship victory March 3. About 300 students were leaving the gymnasium when gunfire erupted, police said.
CBS affiliate station WTOC reports that both the Savannah Police Department and the School Board police are working on the case.
"We're not going to be so much concerned over jurisdiction here, as we are about bringing whoever committed this to justice," said Burnsed.
"One individual in one group produced a weapon and starting firing and hit three individuals in another group," Police Lieutenant Richard Zapal told CBS News Correspondent Steve Kathan.
Officials planned to dispatch counselors to the school Monday to help students cope with the shooting, he said.
"It's a sad situation," Daisy Richards, a grandmother of two Beach High School seniors, said as she and other parents stood outside the school after the shooting. "These kids have just as much a right to celebrate their victory as anyone else. Why, why, why, don't they get these guns away?"