Police identified the victim as Ryan McDonald, a sophomore who lived with his grandmother and had alopecia, a condition that left him bald and the target of endless teasing as a child.
"He tried to have a tough exterior, like a shield, to fit in," his uncle Roger McDonald said. "He was a good kid ... who was dealt some bad cards in life."
The shooting happened shortly after 8 a.m. at the Central High School cafeteria, Chief Deputy Bill Roehl said, and the suspected shooter was taken into custody minutes later on a nearby street. The suspect and victim knew each other, Knox County School System Superintendent Bill McIntyre said.
Jamar Siler, 15, was charged with one count of first-degree murder and was being held in a juvenile court facility, police spokesman Darrell DeBusk said. Silar had an initial appearance in Juvenile Court late Thurday, but his lawyer, public defender Mark Stephens, refused to discuss the case.
"This wasn't a shooting that was a random act," Roehl said. "It was an individual directing his aggression toward another individual, not the school or the students inside the school."
The cafeteria was a popular place to gather before classes started at 8:30 a.m., students said. Chad Griffin, 15, and Josh Matthews, 14, said that they were sitting about 10 feet away from the victim and talking when they heard a sharp noise.
Griffin at first thought someone had dropped a book and then looked around.
"He got shot and started walking and he was holding his chest. There was blood everywhere. And then he fell and his arm hit me," Griffin said.
Matthews said he thought it was a fake at first but then realized the shooting was real.
"I took off running and ran outside and called my mom," Matthews said.
Students in the cafeteria began crying and scrambling to leave, while others tried to get in the room, thinking they had missed a fight, witnesses said. Students began to gather around the victim, said freshman Jared Wohlford, 14. "Everybody started running out real fast saying, 'He got shot,"' he said.
Student Devin Dial, a junior, told the Knoxville Sentinel News that she witnessed the shooting.
"I saw (the wounded boy) go to the ground and start shaking," she told the newspaper.
The school, which has about 1,400 students, was placed on lockdown after the shooting. Classes were dismissed and students were bused to a nearby church so they could be picked up by their parents.