It happened just after 8:00 a.m. Friday while the bus was parked in front of the Hamilton School in the area of 57th and Pine.
Investigators say Tyome Petter, the 15-year-old gunman, is in custody after shooting 17-year-old Chris Taylor in the head. Taylor was last reported in serious but stable condition at Children's Hospital with his family by his side.
After the shooting, the bus driver said Petter then went to the front of the bus and put a gun to his head, ordering him to open the door. He did.
Chopper 6 HD was overhead as Petter was taken into custody about two hours after the shooting. Police say he was still carrying the weapon, a .22 caliber handgun, when he was arrested.
The bus was taking about 10 students CEP Miller Disciplinary School at 43rd and Westminster, where both Petter and Taylor are students. The bus was still about 13 blocks away when the shooting happened.
Action News spoke to Nijul Porter, a student who was sitting in the very next seat.
"I heard it, I was right there. I thought I got shot," said Porter, who added he believed the shooting was an act of revenge following an argument on Thursday.
"He told him to watch his back," Porter said.
Petter was being questioned by police at Southwest Detectives, and he is expected to be charged as an adult in this case.