The arson happened on July 1 in the 2400 block of South Sawyer Avenue in the Little Village neighborhood.
A man and woman were hurt. Police said Thursday that a Chicago firefighter was also injured by the blaze.
A 60-year-old woman suffered smoke inhalation and was taken to Mount Sinai Hospital in critical condition while a 62-year-old man suffered minor injuries and was also taken to Mt. Sinai, officials said.
When the fire happened, investigators said they were looking into reports that gasoline was found at the scene.
A 25-year-old man is now charged with arson.
No further information was immediately available.
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Chicago Sun-Times Media Wire contributed to this report