Cook County Sherriff Tom Dart said hostage takers shot twice through a door as officers stormed up a stairway in an ultimately successful rescue attempt at a home in Harvey.
He spoke to The Associated Press Wednesday, hours after SWAT teams freed two women and two children.
In continuous phone contact during the 20-hour standoff, Dart said, gunman threatened to kill all the hostages. He said talks alternated "from idle talk to threats," and by morning, authorities felt they needed to go in.
Dart said nobody was on a first floor as a SWAT team entered. Shots were fired as officer headed up stairs to the second floor, but no one was hit. He said officers immediately burst through the door and subdued the hostage takers.