Agents released a surveillance photo of the person they're looking for. The FBI says he most recently hit Chase branches. The latest was Monday.
The feds say he's robbed seven banks just since Thursday.
He's called the Swine Flu Bandit because he covers his face with a painter's or surgical mask during his robberies.
At 9 a.m. Monday, he is believed to have robbed the branch at 1130 W. Taylor St. and at noon struck the branch at 4809 S. Ashland Ave.
Additionally, he is believed to have robbed the branch at 550 S. Dearborn St. on Saturday morning and the branch at 4141 W. 95th St. in Oak Lawn last Thursday afternoon.
Eight robberies took place in Chicago, one in Oak Lawn and one in northwest Indiana.
The Swine Flu Bandit is described as a white man, 25-35, 5'6"-5'8" with a thin build, black hair and brown eyes. He has worn a cap or hooded sweatshirt and sunglasses during each robbery.
On at least two occasions, he told suspicious bank employees who confronted him when he entered the bank that he was recovering from the swine flu, the FBI said.
The Sun-Times Media Wire contributed to this report.