The 14-year old freshmen at SuccessTech Academy alternative school had been suspended for fighting, reports CBS News correspondent Dean Reynolds.
"When he got suspended, he said 'I got something for you all,' and I thought he was just playing 'cause he says it all the time," said a fellow student. "But I see that he was for real."
"He's crazy. He threatened to blow up our school. He threatened to stab everybody," Doneisha LeVert said. "We didn't think nothing of it."
Asa H. Coon was armed with two .38 caliber revolvers, and police found a duffel bag stocked with ammunition and three knives in a bathroom, officials said. Parents were angry that firearms got into a school equipped with metal detectors that students said were intermittently used.
Officials said two teachers and two students were shot, and that a 14-year-old girl fell and hurt her knee while running out of the school.
Witnesses said the shooter moved through the converted five-story downtown office building, working his way up through the first two floors of administrative offices to the third floor of classrooms. Officials said he was wearing a black Marilyn Manson concert shirt, black jeans and black-painted finger nails.
"He just came back and started shooting at people," a student tells CBS News. "He would just shoot at anybody who was in the hallway, so everybody just ran down the hallway."
The first person shot, student Michael Peek, had punched Coon in the face right before the shootings began, said student Rasheem Smith, 15.
Coon "came out of the bathroom and bumped Mike and he (Mike) punched him in his face. Mike started walking. He shot Mike in the side." Peek, 14, didn't know Coon had a gun, Smith said.
Antonio Deberry, 17, said he and his classmates hid under laboratory tables and watched the shooter move down the hallway. "I saw him walking past. He didn't see us, we saw him." The shooter swore and shot several times, Deberry said.
LeVert said she hid in a closet with two other students after she heard a "Code Blue" alert over the loudspeaker. She said she heard about 10 shots.
Darnell Rodgers, 18, was walking up to another floor when the stairway suddenly became flooded with students.
"It took me a couple of minutes to realize that I was actually shot, when I felt my arm burning in the area, that's when I realized that I had got shot," Rodgers said.
"They were screaming, and they were saying, 'Oh my God, oh my God.' I knew something was wrong, but thought that it was probably just a fight, so I just kept going," Rodgers said.
Rodgers was released from a hospital after treatment for a graze wound to his right elbow.
Coon had been suspended since Monday for fighting near the school that day, said Charles Blackwell, president of SuccessTech's student-parent organization. He did not know how Coon got into the building Wednesday.
Blackwell said that there was a security guard on the first floor, but that the position of another guard on the third floor had been eliminated.
Students and parents described the gunman as troubled, Reynolds reports.
"It could have been avoided, because there were warning signs," said one parent.
Student Frances Henderson, 14, said she often got into arguments with Coon, who once told her, "I got something for you all." He was a "gothic" who usually wore a trench coat, black boots and a dog collar, she said.