Nicole Harris spent seven years in prison after confessing to the crime, but almost immediately she said she was coerced.
In 2005 Harris stood accused of a horrendous crime: killing her 4-year-old son Jaquari.
Police, then prosecutors, claimed Harris strangled him with an elastic band from a bed sheet because he wouldn't stop crying.
She confessed, but only after 27 hours of interrogation.
"How do you say you did something you did not do? I never understood it until it happened to me," she said.
For seven years, Harris fought for freedom from behind bars. In December, a federal judge decided a state court erred when testimony from Jaquari's then 5-year-old brother was barred. He witnessed the death and said from day one that it was an accident. His mom wasn't even home.
Monday, prosecutors went one step further in formally declaring they will not re-try Harris for he son's death.
"I was ecstatic, just glad to be finally free," Harris said. "There's nothing hanging over my head anymore."
Harris' interrogation took place six weeks before state law changed, requiring police videotape interrogations in homicide cases from start to finish.
Jurors only saw the final 18 minutes of Harris' 27 hours with detectives.
"What a difference those six weeks would have made," said Alison Flaum, Center on Wrongful Convictions.
What is Harris' take on the criminal justice system?
"That it can be flawed and that there are some officials who operate with good intentions and there some that don't and unfortunately false confessions do happen," she said.
A Chicago Police polygraph examiner by the name of Robert Bartik was involved in Harris' interrogation. She claims he called her a monster, a liar and told her she had failed the lie detector, which Harris says drove her to falsely confess.
A Tribune investigation found officer Bartik was involved in five of six murder cases in which defendants were later cleared.
Monday, a police spokesman told ABC7 that officer Bartik is still on the job and still working in the polygraph unit.