The FBI responded to a robbery at Burling Bank at 141 W. Jackson around 2 p.m. They said the suspect fled after a dye pack burst.
Police received an unconfirmed report that the robber may have entered Harold Washington Library, just a few blocks southeast of the bank.
Officers were seen going in and out of the building but said a search of the library and review of surveillance video did not turn up any sign of the suspect.
The suspect is described as a white male with brown hair, 35 to 45 years old, between 5 ft. 2 in. and 5 ft. 6 in. tall, and weighing roughly 115lbs. Surveillance photos from previous robberies show the suspect wearing a white sleeveless shirt, a brown hat and plaid shorts. He also has a tattoo on his right bicep and brown facial hair.
The suspect is believed to be responsible for two other bank robberies in the Chicago area; the first on June 25 at the US Bank at 2263 S. Wentworth Avenue just after 2 p.m., and the second on June 26 at Citibank at 180 N. Michigan Ave, also just after 2 p.m.
The FBI is offering a reward of up to $1,000 for information leading directly to an arrest of the unknown subject.
Anyone with information should call the FBI's Chicago Field Office at (312) 421-6200.