Patricia was jailed for poisoning her son. But there had been a horrible mistake.

September 5, 1989. Patricia Stallings, 24, was getting out of her car at her home in Arnold, Missouri, when the police officers approached. They told her to stop where she stood, and produced a set of handcuffs.

“You’re under arrest for assault.”

Patricia’s alleged victim was fighting for his life in hospital with a suspected case of poisoning. His name was Ryan. He was just five-months old. He was her son.

After Ryan had fallen ill on July 9 that year, Patricia – Patty as she was known to most – and her husband, David, had rushed the little boy to Cardinal Glennon Children’s Hospital. He’d suffered gastric issues since birth, but this was different – he was listless, his breathing was laboured and he was vomiting uncontrollably.

After three days of treatment, Ryan had stabilised. But the diagnosis was devastating. Doctors had found high levels of ethylene glycol in his blood, a compound found in anti-freeze.

“We were split up and talked to by detectives. They immediately started asking me, ‘Is there a problem at home? Are you and David fighting?’ They were saying that they knew that that baby had been poisoned by either me or my husband,” Patty later told Unsolved Mysteries.

“It infuriated me, and I was just… I was devastated. I was blown away… Ryan was my world… He was perfect.”

After almost two weeks in hospital little Ryan was released and placed into foster care while the police investigation was carried out. David and Patty were permitted to visit him for an hour each Thursday.

On the sixth week, Patty spent a short time alone with her son - a matter of minutes. A few days later, Ryan once again fell ill, and he was rushed back to intensive care. As before, the diagnosis was poisoning, and that's when the police pounced on Patty.

While the young mother spent the first of many nights behind bars, her son's condition deteriorated. Two days later, on September 7, 1989, Ryan died in his father's arms.

Patty's charges were upgraded to murder.

The second son, the TV show, the scientist.

While awaiting trial the following February, Patty gave birth to her second son - David Jr. Were it not for this little boy, Patty would likely have died behind bars.

For David Jr also fell sick, just two weeks after birth. His symptoms were similar to Ryan's, yet he was diagnosed with Methylmalonic acidemia - a rare genetic disorder in which the body produces propionic acid, a compound strikingly similar to ethylene glycol.

The police never accepted the possibility Ryan may have had the same condition, and a judge blocked Patty's lawyer from advancing the theory without evidence.

The jury was never told of David Jr's diagnosis, and on January 31, 1991, after 10 hours of deliberation, they convicted Patty of first-degree murder and assault. She was sentenced to life in prison, without the possibility of parole.

The following May, the episode of Unsolved Mysteries featuring Patty aired. And according to University of Michigan's National Register of Exonerations, a man named William Sly happened to be watching.

William was the chairman of the biochemistry department at St. Louis University. Suspicious that Ryan could well have MMA, he asked Dr James Shoemaker, the director of the university's metabolic-screen lab, to test frozen samples of Ryan's blood serum.

Dr Shoemaker found evidence that Ryan did have MMA. The original lab reports had been wrong.

The findings were backed by Piero Rinaldo, a renowned geneticist from Yale University, who conducted his own six-week investigation.

On September 20, 1991, the charges against Patty were dismissed, and David Jr was returned to the custody of his parents.

“We can’t undo the suffering the Stallingses have endured during this ordeal, and I apologise,” Prosecutor George B. McElroy III said in a statement, according to People. “I hope their lives will be happier and fuller in the future.”

Though Patty ultimately filed (and won) lawsuits against the hospital and the lab that tested her son's blood, she told People in 1991 that she wasn't bitter about what happened to her, about the 14 months she spent in prison.

“I have never really been angry,” she said. “I am more damaged.”