INDIANAPOLIS -- Surveillance cameras could unlock the mystery of who shot a 15-year-old boy on an IndyGo bus over the weekend.

The boy, Kevin Gladney, was shot Saturday evening during an argument on a bus near downtown.

Police said the incident began near 12th and Meridian streets, when the driver heard loud swearing in the back of the bus.

The driver pulled over at 14th and Meridian, and that's when a shot rang out, striking Kevin Gladney in the chest.

Police said a passenger who had just gotten onto the bus apparently stepped on a woman's foot as he went toward the back of the bus. According to officials, Gladney was sitting next to the woman and came to her defense.

The shooter fled the scene. Gladney was listed in fair condition Sunday at an Indianapolis hospital.

Police said the shooter used a silver handgun. He was described as black, between 18 and 20 years old, about 5 feet 8 inches tall with a slender build. At the time of the shooting, he might have been wearing a gray hoodie.

Police asked anyone with information to call Crime Stoppers at 317-262-TIPS.

About 20 people were on the bus at the time of the shooting. They were transferred to another bus.

According to IndyGo, the driver followed proper procedure and immediately opened all doors.

"Nothing of this nature has occurred before as far as we know on our bus," said Gil Holmes, president and CEO of IndyGo. "We feel very comfortable that we're doing what we can do at this point. We see this as an isolated incident."

Police are reviewing surveillance video from the bus. The buses are equipped with seven cameras, five inside and two outside that pick up both video and sound.