 -- A 17-year-old started shooting "indiscriminately" after exchanging words with another young man at a suburban Pittsburgh mall, wounding two bystanders as well as his alleged intended victim, police said.

The shooting occurred Saturday evening, just as Monroeville Mall security were starting to respond to a reports of a large group of teenagers becoming disorderly in the Polo section of the Macy's Department store, according to the criminal complaint released today.

Police said Macy's surveillance video showed the suspect firing a gun just as a couple, accompanied by their son, crossed between him and his apparent intended target.

The alleged shooter wasn't found at the scene, but investigators matched store surveillance video to a picture posted to Instagram about four hours before the shooting to identify the suspect as Tarod Thornhill, police said.

Thornhill was later arrested on three counts of aggravated assault, four counts of recklessly endangering another person, risking catastrophe and other charges. He is being charged as an adult and was taken to the Allegheny County jail to await arraignment, according to police.

Police identified the alleged intended victim as Davon Jones, 20, and the wounded bystanders as Mary Singleton, 47, and John Singleton, 48.

The victims were taken to Forbes regional hospital, where the two men were listed in critical condition and remain in the ICU, while the woman is in fair condition, officials said. All three are expected to survive, officials said.

Josh Vehar, a man at the mall with his 5-year-old daughter, told ABC News he saw a young man firing into a crowd of people. He said he was in the Mr. Rogers' Neighborhood Play, about 20 to 30 feet away from where the shooting took place at the Macy's department store.

"I watched this kid pull his gun out and when he pulled the gun out, he just started firing," Vehar said. "He shot like six, seven times and then it just turned into pandemonium after that."