The boy was detained just after the shooting at Heath High School, said Karen McCuiston, a spokeswoman for the school district. He was charged as a juvenile with murder, attempted murder and burglary.
The only words the boy said afterward were "I'm sorry," Principal Bill Bond said.
A witness, Ben Heady, 17 said: "I hear gunshots, about 10 in a row, just bang, bang, bang, bang, bang ... people were just laying on the ground. People were screaming, running out of the hall."
The leader of the prayer group, a pastor's son, walked up to the boy as he was firing, imploring him to stop, Mr Bond said. The boy kept firing but finally stopped and lay down the gun, one bullet left in it. Mr Bond arrived about that time and picked up the gun.
A 15-year-old girl who died about 45 minutes after the shooting was among eight pupils who were taken to hospital. One wounded pupil was treated and released.
Sheriff Frank Augustus said the boy acquired the gun used in the shooting during a burglary at a home on Thanksgiving Day.
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