CHICAGO (CBS) — Melissa Calusinski’s quest for a new trail in the death of a toddler she was watching at a daycare center in 2009 moved to the Illinois Appellate Court on Wednesday, as her attorneys sought to convince three judges her trial was unfair.

Calusinski’s attorney, Kathleen Zellner, argued prosecutors withheld critical evidence at the trial in the death of 16-month-old Benjamin Kingan.

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At a hearing before a panel of three appeals court judges, Zellner said a condensed version of Benjamin’s X-rays made it impossible to see his skull had not been fractured.

“This is a game changer. This is new evidence. It was evidence that wasn’t disclosed. It’s the most frequent area of reversal in the case law. So we’re optimistic,” Zellner said after the hearing.

The defense said a noted radiologist, shown the clear X-rays after trial, saw no evidence of a skull fracture.

“He’s not saying maybe there’s no skull fracture. He’s saying it’s impossible for there to have been a skull fracture,” Zellner said.

Appellate prosecutor Mary Beth Burns argued trial prosecutors turned over all the evidence in the case, and said nothing prevented the defense from going to a computer expert to get a clear look at the X-ray if the image they had was unreadable.

Burns also noted multiple prosecution witnesses testified Benjamin suffered a skull fracture. She said the defense argument that the X-ray shows no skull fracture is not compelling enough “to undermine a verdict that was based on a significant amount of medical testimony.”

Prosecutors argued a preponderance of evidence, including Calusinski’s confession, led to her conviction.

Defense attorneys have said Calusinski’s confession was coerced.

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Calusinski, who has a low verbal IQ, said detectives broke her down after six hours of interrogation and nearly 80 denials, and she only told them what they wanted to hear. She called her interrogation “a nightmare,” and insists she never did anything violent, and never struck Benjamin.

Zellner said the original X-ray files Calusinski’s attorneys received before her 2011 trial were compressed to the point they were not legible, and newly discovered X-ray images showed Benjamin did not have a skull fracture when he died, but instead had a pre-existing head injury.

In July 2015, Lake County Coroner Thomas Rudd changed the official cause of Benjamin’s death from “homicide” to “undetermined,” citing the new X-rays. He said a previous injury caused the boy’s skull to enlarge at an alarming rate. In September 2008, his head size was in the 50th percentile, then the 75th percentile in December 2008 and the day after he died, January 15, 2009, the 95th percentile.

Dr. Eupil Choi, a pathologist who testified at Calusinski’s trial, has admitted he made a mistake, and that he missed a previous head injury during his autopsy on Benjamin.

However, Choi has said he wouldn’t change his mind that Kingan died from a severe head injury caused on the day he died. And prosecutors argued the X-rays cited by Zellner were not new evidence, but images the defense could have enhanced before trial.

After the hearing, Calusinski’s father said he’s more optimistic than ever his daughter will go free.

“I actually think, and I hope, and I pray that this is the end; because enough is enough. My daughter’s suffered so much. She’s been in prison for something she didn’t do,” he said. “I just pray to god that these judges see that the evidence is in front of them. They heard what they heard today. They read theh brief. They read the evidence. It’s the evidence that I believe is going to set my daughter free.”

Zellner said, even if the appeals court doesn’t grant Calusinski a new trial, they plan to keep fighting. That would mean taking the case to the Illinois Supreme Court.

Two years ago, the judge who presided over Calusinski’s trial denied a request for a new trial, ruling there was not enough new evidence to overturn her conviction. Judge Daniel Shanes said the defense did not prove there was any new evidence that would require him to throw out the verdict.

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The appeals court panel hearing Calusinski’s case will rule on her bid for a new trial at a later date. Calusinski is serving a 31-year prison sentence for murder.