Police said Thursday they are also questioning the baby's father.
RELATED: Good Samaritans save newborn left in trash can in Chicago, take him to fire station
A woman and her daughter noticed the baby boy who was just hours old in the 1700-block of North Keystone Avenue on Tuesday. They rushed him to a nearby firehouse where paramedics performed life saving measures on him.
The infant was taken to a hospital in critical condition where his condition has since stabilized.
WATCH: Paramedics urge mothers in desperate situations to 'come to us'
A Chicago family had hoped the baby may lead them to a missing pregnant teenager. Marlen Ochoa-Uriostegui, 19, was last seen on April 23 after leaving Latino Youth High School in Pilsen. She was nine months pregnant when she went missing and had a May 5 due date.
Ochoa-Uriostegui's family called for a DNA test to be performed to identify whether or not she is the mother of the baby. Police said the girl they are talking to Thursday is not Ochoa-Uriostegui.
Ochoa-Uriostegui is described as 5'3, with brown hair and brown eyes, and sometimes wears a small nose ring. She was last seen wearing a gray sweater, sweatpants and a maroon top with a Latino Youth High School logo on it.
WATCH: Pregnant teen, 19, last seen in Pilsen
Illinois is a state with a Safe Haven Law, meaning anyone can hand over a baby 30 days old or younger that is unharmed to staff at a hospital, police station, or fire department, with no questions asked.
Safe Haven babies go directly to adoption agencies so they can quickly find a forever home. Because the baby found in the alley was abandoned illegally, he will go to into the foster system.
To contact the Baby Safe Haven Hotline, call 888 510-2229, or you can visit Safe Haven or Safe Haven Abandoned Babies.