The baby remains at the children’s hospital, where he’s in critical condition but is steadily improving.
Chicago police said they haven’t determined who abandoned the baby.
Fitzmaurice said expectant women can call 911 and not experience judgement, WGN-TV reported.
"I don't know what it's like to have a child, be pregnant and be in some horrible circumstances where you are driven to do something like this. It almost sounds diabolical," he said. "But come to us, call 911. We would've taken the baby to one hospital and her to another hospital. We won't judge. Don't leave your baby in an alley. Come to a firehouse. Leave the baby there. Give the kid a chance."