The shooting occurred on a northbound 75 bus in the 7600-block of South State Street, just off the Dan Ryan Expressway, in the Greater Grand Crossing neighborhood at about 6:17 p.m., police said.
Police initially said the shooting occurred after there was an argument between a 35-year-old man, an 18-year-old man and an 18-year-old woman on the bus. That statement was retracted and an earlier person of interest in the case has been released.
Surveillance photos show the offender exiting the bus, then pulling out a handgun and firing into the rear of the bus, striking multiple passengers, police said.
Police say the alleged shooter is described as an African American man between 18 and 25 years old, standing approximately between 5 feet, 6 inches and 5 feet, 8 inches and weighing between 140 and 160 pounds. He has a black afro, brown eyes and a dark brown complexion.
He was wearing a black hoodie under a light blue jean jacket, striped jeans and black and white colored shoes, police said.
An 18-year-old man was struck in the chest, arm and stomach and hospitalized and critical but stable condition, police said. An 18-year-old woman was struck in the underarm and hospitalized in good condition.
A 59-year-old man took himself to St. Bernard Hospital with a graze wound to his left side, police said. He has been treated and released.
"Bullets started flying everywhere, four or five shots. And I ducked, sir, I don't know what happened," said witness Cheryl Sparks.
Anyone with information about this person is asked to call Area South Detectives at 312-747-8271.