Police now believe the robber, who got away with an unspecified amount of cash, fled the Heritage Community Bank before they arrived, said Police Chief Elton McClendon.
Authorities initially feared there were hostages inside, but when they entered the bank three hours later, they only found two employees hiding in a downstairs bathroom, McClendon said.
They didn't find a gun or any sign of a suspect, who McClendon described as wearing a black sweat suit, black shoes and carrying a 38 mm handgun.
Dolton village spokesman Sean Howard said authorities had been able to communicate with the workers as they hid in the restroom but never talked to the robber inside the bank.
The incident began shortly before 11 a.m. in this town less than 20 miles south of Chicago. The man, wearing a white fleece ski cap over his face, entered the bank and announced the robbery, McClendon said. A bank teller showed him where the money was while customers and employees lay on the floor, then he left, McClendon said.
Four to five customers and employees were able to flee the building when the incident began, Howard said.
Authorities blocked off several streets around the building as police, FBI agents and the South Suburban Major Crimes Task Force worked to resolve the situation.
Jorge Hernandez, 21, an employee at Pepe's Tacos, a restaurant located near the bank, said two bank employees entered the restaurant around 11:00 a.m. after being instructed to leave the building by their manager.
They described to Hernandez a gunman who had a handkerchief over his face and told him the robber had entered the vault.
"They were scared more than upset," Hernandez said in a phone interview. "They were scared for their co-workers."
Hernandez said he and other employees were locked inside the restaurant on the instructions of police, who also told him to stay away from the windows and hang up the phone.
The two bank employees had previously been escorted out by police, Hernandez said.
The last successful robbery at the bank was in 1990, Howard said.