CAN NEWLY DISCOVERED EVIDENCE FREE A DAY CARE WORKER SERVING 31 YEARS IN PRISON FOR KILLING A TODDLER?

"48 HOURS: BLAMING MELISSA" - Saturday, July 18, 9:00 PM, ET/PT

Can newly uncovered evidence free a young Illinois woman sitting in prison for a crime she swears she didn't commit? And if Melissa Calusinski didn't do it, why did she confess multiple times during a police interrogation?

Erin Moriarty and 48 HOURS investigate new surprising developments in the case against Calusinski for the 2009 death of a 16-month-old boy in her care at a suburban Chicago childcare center, in an updated edition of "Blaming Melissa," to be broadcast Saturday, July 18 (9:00 PM, ET/PT) on the CBS Television Network. ("Blaming Melissa" is the first of a 48 HOURS double feature. It will be followed at 10:00 PM, ET/PT by a broadcast of 48 HOURS: "The Girl Next Door.")

"I don't know exactly what happened to him," Calusinski told 48 HOURS. "But I got blamed for it."

The story begins in 2009, when, according to Calusinski, young Ben Kingan started falling asleep when he should have been awake. Calusinski tried to wake him, but he was unresponsive. She called for help. Her sister, Crystal, began CPR. Ben died. Two days later, Calusinski was questioned by police. Police told her she was the last adult to see Ben alive and that the toddler died from a blunt-force trauma to the head. Calusinski was interrogated for nine hours, never asking for a lawyer. Then, she confessed to dropping the child in a way that may have led to a head trauma.

Calusinski was tried and convicted of murder, largely on the fact that she confessed, and that the pathologist who did the autopsy said the child had suffered a skull fracture, even though he had no open wounds or serious bruises.

"I believe we had sufficient evidence to show that she, in fact, killed Benjamin that day," Assistant State's Attorney Stephen Scheller told 48 HOURS.

But now, in a twist out of a mystery novel, an anonymous caller told Calusinski's father that there was a set of X-rays not seen at the trial. Those X-rays, according to current Lake County Coroner Dr. Thomas Rudd, indicate the child didn't die in the manner portrayed at trial. According to Rudd, "There's definitely no skull fracture here." Rudd also changed Kingan's official cause of death from homicide to undetermined.

"This is medical evidence that was withheld," says Chicago attorney Kathleen Zellner, who believes Calusinski was wrongfully convicted. "And it was deliberately withheld, because the person who called knew it had been deliberately withheld."

Zellner specializes in wrongful convictions and successfully fought for the release of Ryan Ferguson, a Missouri man convicted of killing a local newspaper sports editor. Ferguson was freed from prison after 13 appeals.

Why would Calusinski confess? "I've never been in a situation like that, ever," Calusinski told 48 HOURS. "I didn't even know what was going through my mind."

Was Calusinski wrongfully convicted or did the jury get it right? Moriarty and 48 HOURS piece together the incident and the case against Calusinski through interviews with Melissa, her father and sister, Zellner, Assistant State's Attorneys Stephen Scheller and Matthew DeMartini, State's Attorney Michael Nerheim, Rudd, and newspaper reporter Ruth Fuller. 48 HOURS: "Blaming Melissa" is produced by Gail Abbott Zimmerman. Charlotte A. Fuller is the field producer. Judy Tygard is the senior producer. Susan Zirinsky is the senior executive producer.

"Blaming Melissa" will be followed by a 10:00 PM ET/PT encore of "The Girl Next Door," featuring Moriarty and 48 HOURS' investigation into the murder of Hunter Grissom in an Alabama parking lot and the case against his wife, Tracy Grissom. She maintains she shot him in self-defense after being abused. Prosecutors, and Grissom's family, maintain she killed him in cold blood. 48 HOURS: "The Girl Next Door" is produced by Chris Young Ritzen, Susan Mallie, Judy Rybak and Marc Goldbaum. Al Briganti is the executive editor. Susan Zirinsky is the senior executive producer.

Chat with members of the 48 HOURS team during the broadcast on Twitter and Facebook. Follow 48 HOURS on Instagram. Listen to 48HOURS podcasts at Play.it.