Police said Thursday they are also questioning the baby's father. It's unclear if either will face any criminal charges as prosecutors will have to determine the next steps based on what the two juveniles told detectives.
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"We were able to track down all of them, so we know who the father is, the grandparents the mom," said Chicago Police Superintendent Eddie Johnson. "It's a tragic incident, of course it turned out good because the baby survived and is doing well, but those things don't have to happen."
On Tuesday, a woman and her daughter noticed the baby boy who was just hours old in the 1700-block of North Keystone Avenue. 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'
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.
"They can walk away," said Dawn Geras of the Save Abandoned Babies Foundation. "They don't have to answer any questions. There won't be police coming to look for them. The baby will be loved forever."
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.
The conclusion of the case means a heartbreaking reality for another Chicago family. They had hoped DNA from the abandoned baby would lead them to 19-year-old Marlen Ochoa-Uriostegiu, a pregnant mother who was set to give birth just days ago. She vanished two weeks ago. Now their hopes are dashed.
WATCH: Pregnant teen, 19, last seen in Pilsen
"We were hoping that we were getting close to finding Marlen," said Emma Lozano, a family spokeswoman. "We're frightened that maybe something terrible has happened and we just need people to keep the faith and keep looking for her and not to give up."
Ochoa-Uriostegiu 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.