Produced by Gail Abbott Zimmerman

[This story first aired on Feb. 28, 2015. It was updated on July 18.]

There has been an extraordinary new development in a case "48 Hours" first aired in February. It began with an anonymous phone call that led to new evidence that could mean everything to a young day care worker blamed for a child's death.

(CBS) Lincolnshire, Illinois -- Assistant State's Attorneys Matt DeMartini and Stephen Scheller say 16-month-old Benjamin Kingan should not have died on Jan. 14, 2009.

"There's no victim more innocent than a -- a toddler," DeMartini said. "A toddler is free of sin."

"He was a very ... healthy baby," Scheller added. "...just a happy happy little boy."

Ben Kingam Daily Herald



And Ben, they say, came from a happy home, with devoted parents.

"They are very private. ...and they are -- some of the sweetest people you could meet," DeMartini said. "They spent time with their kids and they were just loving people."

Both held professional jobs, so Ben, his twin sister, and their two older siblings went to the Minee Subee day care center in an affluent Chicago suburb.

"How would you describe what the parents have gone through?" Moriarty asked.

"When somebody takes your child from you, I don't think there's any words to describe what they've gone through," said DeMartini.

The Lake County, Illinois, prosecutors blame a young woman for Ben's death: Melissa Calusinski. She was 22 years old at the time, working as an assistant teacher.

"I would never, ever hurt a child," Melissa told Moriarty. "I would never put my hands on anybody."

Melissa Calusinski Paul Calusinski

From the outset, she was an unlikely murder suspect: no criminal history and no disciplinary problems in school.

"I've never been in trouble," said Melissa.

The youngest of five children in a close-knit family, she was especially tight with her sister, Crystal.

"She's very gentle, genuine," Crystal Calusinski said. "If you tell her to do something, she would do it, like, in a heartbeat."

Yet, Crystal Calusinski admits Melissa isn't quite like everyone else. Tests show that she has a low verbal IQ, meaning she sometimes has trouble expressing herself and understanding others.

"She was a little bit slower," Crystal explained. "Kids would make fun of her for it."

"What would kids say?" Moriarty asked.

"Just mean things like ... you know, ' You don't know this. You're stupid,'" said Crystal.

"She would come home crying sometimes off the bus. Kids would tease her," said Paul Calusinski.

Their parents, Paul and Cheryl, say that while Melissa did need extra help at school, she excelled at art. And she blossomed when, as a teen, she began babysitting a family of rambunctious boys.

"She wanted to be taking care of children," said Cheryl Calusinski.

So Melissa jumped at the chance to work at that daycare center with her sister.

"Melissa's job was the assistant teacher in the infant room," Crystal explained.

"Have you ever seen her frustrated with a baby or a small child?" Moriarty asked.

"No, never," she replied.

All of the children were fond of Melissa, says Crystal, including Benjamin Kingan.

"A child doesn't come by a teacher or a person that they don't like. They would scream and cry," Crystal told Moriarty. "When Ben went to Melissa he would never do that. ...He trusted ... her."

Which is why Melissa says she was so alarmed that afternoon when Ben did not respond to her.

"Ben was ... sittin' in his bouncy chair, playing with his blanket. ...And then he kind of falls back asleep," she told Moriarty. "When I saw him startin' to fall asleep, I'm like, 'Ben, Ben.' And no response. ...he didn't look right. ...and I touched his hand. He did not wake up at all."

"I flew in there," Crystal said. "And she was, you know ... trying to comfort him.'Ben, wake up.'"

"His hand wasn't moving at all." Melissa said. "It was nothin' I've never seen before from a child."

"I saw orange foam ... coming out of his nose, and -- um I'm sorry," Melissa said in tears.

That's when Crystal raced into the room and administered CPR.

"Just picturing a little child and you're there standing there doing CPR," said Crystal.

"You can't get that outta your head--" Moriarty commented.

"No," said Crystal.

"And what was Melissa doing?"

"She was crying, but she was trying to get the other kids out," Crystal said. "She was just really, really scared."

Paramedics arrived and took Ben to the hospital. Two hours later, Melissa learned Ben was dead.

"Me and my sister fell to the floor, and we're just -- we're just bawling," said Melissa.

"Well, what's going through your mind at that point?" Moriarty asked.

"What happened to him? How did he die?" said Melissa.

It was a mystery. Ben didn't have any gashes or open wounds -- no serious bruises anywhere - only what a toddler might have. It took an autopsy by pathologist Eupil Choi to come up with an answer.

"Dr. Choi indicated that there was ... a blunt force trauma to the head, which -- caused the death of Benjamin Kingan," said DeMartini.

The damage was inside. Choi said there was a skull fracture as well as a large injury in the back of the brain. Police believed whatever happened to Benjamin happened that day at the center. And so they brought in the caregivers who had been with Benjamin and questioned them separately, including Melissa's sister, Crystal.

"They were like, 'What happened to this child?'" Crystal said. "Then they go and say ... 'This is a homicide investigation.' ... And then my mouth just totally dropped."

Cop: Somebody did something ...

"Did you think you were in trouble?" Moriarty asked.

"No, because I know I didn't do anything," Crystal replied.

Crystal Calusinski was finally released after eight hours, but Melissa was still with police:

In the first hours of questioning, Melissa Ca... 02:34



Det. George Filenko|Lake Zurich Police Department: All you need to do is tell us the truth and we're done.

"What did they tell you had happened to Ben?" Moriarty asked Melissa.

"That he died of -- a skull fracture," she said.

Melissa Calusinski: I don't even know what I could have done to hit, to make him hit his head...

"I was trying to help 'em," Melissa said. "...cause they're cops of the law."

Calusinski interrogation: Part 2 02:16



Det. George Filenko: You know 100 percent. We know what happened, but we need you to tell us. Tell us what happened.

Investigators read Melissa her rights. "It's routine and protocol for us," said Det. George Filenko.

But over and over, she denies doing anything to Ben.

Melissa Calusinski: I had nothing to do with it.

But after six hours in that room ...

Det. George Filenko: In a few days it's not going to be credible.

...her story changes and she tells them there might have been an accident:

Melissa Calusinski: 'Cause I put him down and he kind of almost slipped when I dropped him. And he hit the chair.

Calusinski interrogation: Part 2 02:44



Then, after three more hours, her story gets more sinister:

Det. Sean Curran | Lake Zurich Police Department: You get mad at him and you throw him on the floor. Melissa Calusinski: [Nods to affirm] Det. George Filenko: You threw him on the floor? Melissa Calusinski: Yeah. ...Really hard. Det. George Filenko: Really hard? Melissa Calusinski: Yeah.

She is taken to another station for booking and repeats the same terrible story:

Officer Adam Hyde| Lincolnshire Police Department: How hard did you throw him? Melissa Calusinski: I went like that (throws doll down hard)

After spending 14 hours with police -- without her parents or a lawyer - Melissa Calusinski is arrested and charged with murdering Benjamin Kingan.

Although she soon recants, it's too late.

Melissa Calusinski [In police car]: No, I'm innocent.

"I was, like, thinking to myself, 'Is this real? Is this happening to me, for something I didn't do?'" she told Moriarty.

THE CASE AGAINST MELISSA

"It's every parent's worst nightmare," reporter Ruth Fuller said. "You right away wanna hate this girl, this day care worker who was caring for this boy."

When Fuller, then a reporter for the Chicago Tribune, first began covering the case of Melissa Calusinski, she felt the same way most people did about the young woman accused of murdering a toddler.

"The first thing you're told is that this woman murdered him and that she slammed him to the ground," she said.

Fuller's daughter, then in daycare, was around the same age as Benjamin Kingan.

"This one hit home because all I could think of was this could have been my child," she said.

The trial began in November 2011. Melissa Calusinski says she was optimistic and believed that hard medical evidence would prove she was pressured into making a false confession.

Det. George Filenko: We're not going anywhere until we get the facts here.

"I've never been in a situation like that, ever. I didn't even know what was going through my mind," Melissa told Moriarty.

"I believe we had sufficient evidence to show that she, in fact, killed Benjamin that day," said Scheller.

Assistant State's Attorneys Steven Scheller and Matthew DeMartini theorized that Melissa killed out of frustration. They say there was a lot of commotion that day and Melissa was overwhelmed.

"She became frustrated holding Ben," Scheller said. "She threw him to the floor."

Melissa Calusinski: I was feeling so frustrated...

"Could you find any history on Melissa's part of any kind of problems with babies?" Moriarty asked. "Did anyone report that?"

"Not that I'm aware of," DeMartini replied.

But the more Fuller learned, the more she began to question the case against Melissa.

"I realized that Melissa had a story to tell," she said.

Fuller worried about the nine hours it took investigators to get the young woman with a low verbal IQ to confess:

Det. Sean Curran: You threw him on the ground, he hit the back of his head. What happened?

And there was this: Melissa told investigators that when she threw Ben to the floor, another teacher was in the same room - at the sink.

But that teacher, Nancy Kallinger, told police she didn't see or hear anything:

Cop: Melissa ... picked him up and threw him on the ground ... while you were doing the dishes. Nancy Kallinger: Huh? Cop: Those are her own words, OK. Nancy Kallinger: She wouldn't have done that.

"If Nancy was in the room when this happened, you would think that Nancy would've heard it," Fuller explained. "She testified that she never heard kids screaming or crying."

"Did anyone at trial remember seeing Melissa angry or upset with the children?" Moriarty asked.

"No one. And no one ever heard any commotion, any screaming, any crying. No one heard anything," Fuller replied.

"Ben went to sleep, and after he woke up ... the day care workers found a bump on his head ... and pointed it out to his mother," Fuller explained.

How that bump got there is unclear, but Ben's mother showed it to his doctor, who saw no reason for alarm.

"The pediatrician actually examined Benjamin's head, had felt around -- said there was no issues that she felt needed to be addressed, that mom should just keep an eye on him," Scheller told Moriarty. "Ben never had an issue after that."

But defense experts say that after that day, there were possible signs of head trauma -- medical records showing Ben was "lethargic."

Nancy Kallinger: And If I might just point out about Ben ... there's always something up with him.

Teacher Nancy Kallinger told police that he slept a lot.

Nancy Kallinger: He had just gotten up from a 2:30 nap and then he wants to go asleep again at 3:30.... that's something that I thought was very odd about Ben."

And just two days before he died, Ben threw up violently on Melissa.

"This was big vomit. He-- it was, like, nonstop," said Melissa.

Defense attorneys said these were signs of a brain injury that left him vulnerable to any further impact, even a minor one. And Ben did have a habit of throwing his head back and hitting it. Nancy Kallinger said he did that twice shortly before he died.

Nancy Kallinger: I put him on the floor and he immediately threw himself on the floor. ...And I walked towards the sink and he threw himself again.

Prosecutors scoffed at the defense theory. They say Ben threw up because he had a stomach bug.

"Ben became ill at a day care center. He did throw up a couple of times," said Matthew DeMartini.

"More than -- a couple of times, Matt," Moriarty pointed out.

"...he went home and threw up a couple more times. He was given Pedialyte and put to bed. He woke up the next day and he was fine," said DeMartini.

And they insist that Ben's fatal injury happened on the day he died --and that Melissa inflicted it just as she said.

"What she told the police was that she threw him to the floor. And his injuries are consistent with that impact to that floor," said Scheller.

They closed their case with a video of Ben pushing a toy shopping cart taken several weeks after he got that bump on his head. Proof, they said, that he was neurologically fine.

"It's heartbreaking," Fuller said of seeing the video.

"And how much do you think that influenced the jurors?" Moriarty asked.

"Oh, it's huge," she replied.

The jury took seven hours to deliberate.

"They took me back to the courtroom. And I was pretty positive about it. They said they reached their verdict. And ... they said 'guilty.' I just -- I almost lost it," Melissa said in tears.

Guilty of first-degree murder, Melissa Calusinski was sentenced to 31 years in state prison. But her father, convinced Melissa was innocent, vowed to fight for her.

"... anything for my daughter," Paul Calusinski said. "I just couldn't stop."

He persuaded a newly elected coroner to take a fresh look at the case and he found something he never expected.

EXAMINING THE EVIDENCE

Melissa Calusinski, 27, spent four years behind bars before Dr. Thomas Rudd, the new Lake County coroner - who is currently running for re-election -- took a look at the autopsy evidence.

"I could not believe what I was seeing, because it was the exact opposite of what was written. So, I had my head spinning," Dr. Rudd told Erin Moriarty.

At Melissa's trial, state pathologist Dr. Eupil Choi said Benjamin Kingan did not have an old injury, but his own slides showed that the toddler did.

"I saw a membrane, and I thought, 'my God,'" said Rudd.

"What do you mean when you say you saw a membrane?" Moriarty asked.

"You see a scab. Similar to what forms on your skin except it's in the brain," Rudd explained.

"This is normal," Dr. Rudd explained, pointing to the bottom of the scan. "Everything above this is abnormal and should not be there. Only this should be there." 48 Hours

Holding up a slide of the infant's brain, Rudd points out what is normal versus abnormal on the scan.

Rudd says Dr. Choi made a glaring error when he said Ben was severely injured on the day he died. It's obvious that injury was old, he says.

"This is a membrane, this is a scar tissue, this is a scab," Rudd told Moriarty, referring to the slide. "By definition if you have a membrane you have an old injury."

The autopsy slides - and others he prepared himself - confirmed his findings.

"Every one showed iron ... that is definitive proof that it's an old injury," Rudd explained, pointing out spots on the slide. "Any resident in first-year pathology can recognize this."

And he didn't stop there. Rudd turned to well-regarded pathologist and former Cook County Chief Medical Examiner Nancy Jones for another opinion. She also saw evidence of an old injury - one that had been healing for about two to three months -- a time frame consistent with that bump the day care workers noticed on Ben's head.

"How big was that old injury?" Moriarty asked Rudd.

"Four inch by four inch," he replied.

"Isn't that significant -" Moriarty commented.

"Huge, hugely significant. And how they let that go is beyond me," Rudd replied.

"But you're saying, though, something else did happen on the day Ben died?" Moriarty asked.

"Correct. ...A minor injury. He could have just twisted his head really fast," Rudd explained. "The added fluid of the recent injury ... pushes that brain down and shuts down the breathing system. That is the -- the cause of the child's death. It was the old injury. The old injury was massive."

Both doctors Rudd and Jones believe that injury had been exacerbated by "cumulative incidents of head banging."

"He was what we call a head banger," said Rudd, who felt he had to act.

"At some point did you reach out to Dr. Choi?" Moriarty asked.

"Yes, that was very interesting," he replied.

Asked if he was nervous about it, Rudd said, "Yes ... I thought for a very long time, 'How will I do this?'"

Dr. Choi's affidavit

To Rudd's relief, Dr. Choi admitted he was wrong. He even signed a sworn affidavit, conceding that, "in my report and testimony I missed that Ben had suffered an old injury..." but he crossed out the word "significant."

"I've never seen the key pathologist for the State give an affidavit after the trial, after the conviction, saying, 'Whoops, I missed that prior injury,'" said Kathleen Zellner.

That affidavit is a game changer says Melissa's lawyer, Chicago attorney Kathleen Zellner. She's built a reputation for getting wrongfully convicted people out of prison -- including Ryan Ferguson.

Zellner says Melissa did not get a fair trial.

"The end goal is to find out if this conviction has integrity. I don't believe it does," she said.

When confronted with Dr. Choi's admitted mistake, prosecutors Matthew DeMartini and Steven Scheller concede there was an old injury, but they now say it was too small to matter.

"The microscopic injuries are just that, microscopic. There's no indication that anything in there is significant," DeMartini reasoned.

Rudd disagrees, saying he didn't even need a microscope to see it.

"Was that scar... in Ben Kingan's brain, was that visible to the naked eye?" Moriarty asked the coroner.

"Yes, it is," said Rudd.

"Just doing the autopsy you should have been able to see it?"

"That's correct," Rudd replied.

He also questions that skull fracture Dr. Choi reported seeing. Rudd believes it may have just been a normal part of Ben's growing skull.

"The alleged fracture was right in the middle of the head and towards the right going one inch," said Rudd, pointing to the spot on top of his own head.

"And there's no laceration there? There's no bruise -" Moriarty asked.

"None. None. Whatsoever," said Rudd.

"Is that possible then?"

"Highly unlikely. Highly unlikely. How do you fracture a skull without causing tissue damage to the skin above it? It's not possible," said Rudd.

He says he can't prove there was no fracture because Dr. Choi didn't preserve that evidence. Rudd could only look at photos. And as for that video prosecutors relied on at trial? Rudd says it's impossible to tell whether Ben had an injury then.

"Are you saying that Ben Kingan could have had a serious injury at the end of October and still been seemingly OK for two months and then just die?" Moriarty asked Rudd.

"Easily. Yes," he replied.

He says Ben's parents and doctors may have had no reason to suspect a serious injury.

"A child who can't talk can't tell you that, 'I feel nauseous' or 'I have headaches' or 'I can't see well. I've got blurred vision,'" said Rudd.

"You're confident, even though Dr. Choi made a mistake, filed an affidavit, that this was a fair trial?" Moriarty asked Scheller.

"I'm confident, based on all the evidence that the jury heard, that Melissa Calusinski killed Benjamin Kingan," he replied.

Melissa Calusinski: I feel like it was my fault. Yes I do.

After all, prosecutors say, Melissa Calusinski herself said she did it. In Rudd's eye, that's all that's left of their case.

"I do not see any evidence that she did it other than her confession," he said.

A TROUBLING CONFESSION

Det. Sean Curran: ...he starts acting up and you get mad at him and you throw him on the floor... Det. George Filenko: You threw him on the floor? Melissa Calusinski: Yeah ... really hard. Det. George Filenko: Really hard? Melissa Calusinski: Yeah.

Melissa Calusinski says she still can't explain why in 2009 she told police she killed Benjamin Kingan and even demonstrated how she did it.

"Do you understand why the state's attorney thinks this is a true confession? Is this a confession?" Moriarty asked Melissa.

"That is not a confession," she replied.

"What is this?" Moriarty asked.

"That's a bunch of lies," she said.

But it doesn't look or sound like a lie:

Det. Sean Curran: Show us how hard you threw him on the ground. Melissa Calusinski: I went like that. [Slams a folder to the ground]

"It does seem very convincing," Moriarty noted. "Why would she say she did slam the baby down?"

"It's very difficult to get inside of the mind of somebody under that kind of pressure," said Melissa's attorney, Kathleen Zellner. "It's easy from the outside to say, 'Oh, I'd never do it.' And then the answer is, 'Yeah, but you've never been in that spot.'...You haven't been pinned in a room with these two big detectives. ...You've never been the last one in a room with a child that's dying."

When Melissa went into that interrogation room, she says she'd barely slept in the two days since Ben died.

"It was, like, mentally exhausting for me," she told Moriarty. "I mean, a child just died. ...And it takes time to heal. I'm an emotional person when any type of bad thing would happen."

Det. George Filenko: We're gonna give you another opportunity... to either be a good witness or a co-conspirator in a murder.

"This was a really, really rough interrogation on a woman who could not withstand this kind of interrogation," said Fuller.

Det. George Filenko: That story you're giving us is a load of s---...

"There were times that the police got in her face, yelling expletives and slamming their fists," said Zellner.

Newspaper reporter Ruth Fuller says this is the most troubling confession she has ever seen.

"Almost any person I've ever asked has said to me, 'I would never confess to something I didn't do. Are you kidding me?' People don't believe that it can happen," she said.

But false confessions do happen. The Innocence Project found that more than 60 percent of those convicted of homicide and later exonerated by DNA confessed to crimes they didn't commit -- often after lengthy, intense interviews.

When tested, Melissa showed "extreme vulnerability to suggestion." She scored in the bottom four percent for verbal comprehension.

Melissa Calusinski [crying]: ...'Cause I'm trying to think what did I do...

"They've got her cornered," Zellner said as she watched the interrogation video. "And she's unsophisticated about her legal rights."

Det. George Filenko: If you had a choice right now you'd be as far away from us as possible...

But prosecutors Matthew DeMartini and Steven Scheller say the cops played by the rules.

"She came there voluntarily. She was not in custody of the police ... and she could've left during the interview," said DeMartini.

"Why didn't you walk out?" Moriarty asked Melissa. "Did you know you could?"

"I did not know - anything," she replied.

Video of Melissa Calusinski left alone in the interrogation room. Melissa never ate that day; she didn't even go to the restroom. And she spent long periods alone with no way to contact anyone.

"They would leave and lock the door, and lock me in there," she said.

Over and over, the detectives drive Melissa into first just admitting that she hurt Ben by "accident."

Det. Sean Curran: I do think an accident happened...

Law professor Deborah Tuerkheimer is a former prosecutor who has written about the risk of wrongful convictions in infant head trauma cases.

"People who are innocent often believe ... 'if I can confess to this crime ... down the road, it'll get sorted out, because I didn't do anything wrong,'" Tuerkheimer explained. "Detectives repeatedly told her that they understood how this could have happened; that she wasn't a bad person ... that she simply needed to come clean and everything would be OK.

Det. Sean Curran: You're a good person, I can tell that. Det. George Filenko: We're not here to condemn you. We're not here to put you in jail...

And, after nearly six hours of denials, Melissa finally relents:

Det. Sean Curran: We wouldn't want you to go to jail Melissa Calusinski: Cause I kind of put him down. He kind of almost like slipped when I dropped him. And he hit the chair.

"Did that happen?" Moriarty asked Melissa.

"It never happened," she adamantly replied.

"But you're telling these cops that."

"I know. And I -- I wish I didn't," she said. "But when I kept denying -- they weren't letting me out."

But now, the detectives want more:

Det. George Filenko: The doctor's telling us that there's a lot more to this than just that.

"Every time she came up with a scenario of what could've happened to Ben, the police officers went so far as to have Dr. Choi -- and it's morbid-- but to have Dr. Choi remove Ben's body from storage at the coroner's office and to re-enact what she was saying happened in order to verify whether or not what she said was possible," said DeMartini.

Det. Sean Curran: They just did an experiment ... There's no way that would have cracked his skull.

Based on what Dr. Choi was tellign them, the detectives are convinced that someone deliberately hurt Ben Kingan that day.

"Detectives say such things as, 'The science doesn't lie,'" Teurkheimer said of the questioning.

Det. George Filenko: Medical evidence ... it just doesn't lie.

"We know this happened, because there could be no other possibility," Teurkheimer continued.

Det. Sean Curran: It's a medical certainty... Det. George Filenko: This is absolutely crap. That may have happened ... But that's not what caused the injury.

"The person is only given one option: It is a severe head blow. It wasn't an accident. You had to have done this," Zellner explained.

Det. George Filenko: Something frustrated you. Something happened, OK?

"They kept saying, 'Oh you were aggravated, you were frustrated," said Melissa.

Det. Sean Curran: He didn't do anything to frustrate you? Was this something out of frustration? Melissa Calusinski: [Shakes her head no) Det. Sean Curran: What we think happened here ... We think in this situation the other babies are screaming, crying whatever ... You have Ben in your hands, he starts acting up, and you get mad at him and you throw him on the floor. Melissa Calusinski: [Nods to affirm] Det. George Filenko: You threw him on the floor? Melissa Calusinski: Yeah ... really hard. Det. George Filenko: Really hard? Melissa Calusinski: Yeah.

"You said you threw this baby down hard. Did you, Melissa?" Moriarty asked.

"I did not. I didn't throw him," she replied. "I've always been patient."

Melissa Calusinski: It's frustrating with all these kids 'cause they're screaming, crying...

"And that day, the kids weren't loud. They were all playing," Melissa continued. "They were puttin' the words in my mouth."

"But -- you said it. You're saying they're putting the words in your mouth. You didn't have to say it, did you--" Moriarty pressed.

"I didn't. But see, I -- and I didn't know that. I was just -- I mean ...they wanted me to say that ... so that we could all go home," Melissa replied.

Attorney Zellner says one of the biggest problems with this confession is that it doesn't fit the evidence.

"The injuries are inconsistent with her description," she said.

Melissa told investigators that Ben was facing forward.

"If she's holding him forward, and says she threw him and he hit his head, isn't that a problem?" Moriarty asked Schuller.

"I don't see it as a problem at all," he said.

The prosecutors refused to show "48 Hours" how Ben received his injuries on the back of the head.

"I'm not gonna show you how she demonstrated," Schuller said.

Instead, they said to watch that second confession Melissa gave late that night, where Melissa demonstrates how she threw the baby.

Zellner says Melissa's reenactment proves her point.

"We've got all of the injuries right here," Zellner said, pointing to the back, top right, of a doll's head.

"And any injuries at all on the neck or on the back?" Moriarty asked.

"None to the neck. No bruising. Nothing. So that's not consistent with her demonstration at all," said Zellner.

"I mean, she's so tiny and - look how long this is," attorney Kathleen Zellner said. There's just no way to get that force." 48 Hours



What's more, Ben was a lot heavier than the doll used in the demonstration; he weighed 22 pounds and was 30 inches long. Zeller used a pillow of the same size and weight to demonstrate.

"I mean, she's so tiny and - look how long this is," Zellner said of the pillow. "There's just no way to get that force."

Det. Sean Curran: If you got mad and said, "get on the ground," just tell us.

Melissa told the story detectives prompted her to tell, says Zellner.

Det. George Filenko: Show us how angry you were, and show us what happened, and let's just get this over with and move on.

"She's naive, she's trusting, she's a people pleaser, she's trying to help them resolve this," Zellner said. "She's bargaining to get out of the room. That's what she did."

Melissa Calusinski: I'm trying to make it sound right ... I want to help you guys so much...

"Didn't you realize, if you were admitting to hurting this baby, you weren't going home? You were gonna go to jail," Moriarty asked Melissa.

"I had no idea at all when I was sayin' all that," she said.

"What did you think?"

"I was just tired," Melissa explained. "I was just scared, I was just ready to -- get away from these men."

Remarkably Melissa repeatedly told "48 Hours" she truly believed that if she told detectives what they wanted to hear, they would all just go home:

Melissa Calusinski: ...I'm just kind of curious, how long much more, 'cause ... Det. George Filenko: Not much longer ... We're on the phone right now. We're trying to get this done as quickly as possible. Melissa Calusinski: Because I just want to go home and spend time with my parents and my puppy.

"She has no idea that she has just ended the life that she knew," said Zellner.

Melissa Calusinski: And I'm very, very truly sorry. I didn't mean to get mad at you, with you guys. Det. George Filenko: That's alright, we understand. Det. Sean Curran: That's OK. Melissa Calusinski: So sorry. Det. George Filenko: We understand.

NEW EVIDENCE

For more than six years, Melissa Calusinski's family has waited for her to return home.

"...she liked to do her arts up here," Crystal Calusinski said, showing off sister Melissa's room. "We still have all her clothes ... all her pictures and everything."

They still have the dog that Melissa worried so much about during her interrogation.

"When we try to open this door, I think he thinks she's probably home, that's why he gets he's really excited right here now," she said of the door to Melissa's room.

Crystal Calusinski is determined her son will remember her sister.

"He talks to her on the phone. And just thinks she's away at college - because that's the way we want to keep it at," she said, her voice breaking.

"It's painful, 'cause he's like, 'When can I see you?' You know, 'are you gonna come over to Gran-Gran's?'" Melissa said in tears. "And I was like, 'I am soon.'"

So far, two courts have allowed Melissa Calusinski's conviction to stand.

And Benjamin Kingan's parents, who declined an interview with "48 Hours," say they still firmly believe that the jury got it right.

"The family members of Benjamin Kingan stated through their attorneys, Corboy &Demetrio, that they firmly believe in the integrity and veracity of the police investigation, the interrogation and confession of the defendant, the jury trial and verdict, and the unanimous appellate court decision affirming the jury verdict.

The claimed "new" issues raised in the media and the post-conviction petition are really not new. The very same arguments were made before the jury. The jury unanimously rejected them."

"What would you say to the Kingans?" Moriarty asked Melissa.

"That I had nothing to do with this and that ... you know, I'm sorry for, you know, lying and confessing, saying that I killed your son," she replied.

"They believe you did, don't they?" Moriarty asked.

"They do," she said.

Asked how she feels about that, Melissa told Moriarty, "Horrible. Horrible."

Despite all the questions raised in Melissa's case, State's Attorney Michael Nerheim sees no reason to reopen it.

"I reviewed the case. I reviewed it personally," he said.

Nerheim points to a letter in which pathologist Eupil Choi writes, that, even with his mistakes, his testimony would have been the same at trial.

"You're not concerned ... that one of the most important witnesses at this trial ... admits he made a mistake?" Moriarty asked.

"If his mistake changed the ultimate -- his ultimate opinion, which he hasn't said that it did, that would concern me," Nerheim replied.

"The fact that she said more than 70 times, 'I didn't do it, I didn't do it,' does it concern you at all," Moriarty pressed. "That she might have been worn into saying that, she would try to please these cops --"

"I think that happens in wrongful confessions. I don't think it happened here," said Nerheim.

But then in June, this case took a turn straight out of a novel: Melissa's father got an anonymous call from a man who told him there were X-rays of Ben Kingan that never made it to trial.

"Did you know these X-rays existed?" Moriarty asked Dr. Rudd.

"Did not know they existed and nobody ever told me they existed," he replied.

After getting that tip, Dr. Rudd's staff searched their computer archives and came up with surprising images taken at Ben's autopsy.

"We have his head, his face and his upper chest and upper extremities filmed," said Dr. Rudd.

"What was your reaction when you first saw these?" Moriarty asked.

"I was dumbfounded," Dr. Rudd replied.

What the X-rays show -- or rather don't show -- says Rudd, contradicts Dr. Choi's testimony.

"There's definitely no skull fracture here. I've shown this to various pathologists and a radiologist," Rudd explained. "They've all called me and said 'there is no skull fracture in this child at all.'"

What's more, Rudd says, X-rays of the lower part of the child's body show no evidence of an assault at all.

Benjamin Kingam X-ray Court evidence

"The spine's in good shape. The ribs are in good shape. The upper extremities are in good shape. There are no fractures here. And obviously no fracture here," Rudd pointed out.

"If, in fact, Melissa had thrown the baby down, like she seemed to confess, would the X-ray look the way it does?" Moriarty asked.

"No," Rudd replied.

What the X-rays do show, says Dr. Rudd, is an abnormally shaped head -- another indication of an old injury.

"His head looks like the old-fashioned light bulb. In other words, it's round. Anybody's head that is developing at this age is gonna be oblong," Rudd explained. "This is not a normal-shaped skull of a 16-month-old child."

"What was your reaction when, not only were these X-rays uncovered, but you see what they show," Moriarty asked attorney Kathleen Zellner.

"I felt enormous sense of relief. I thought, 'There is a God. There is a God,'" she replied.

Zellner says that the newly discovered X-rays prove that Melissa Calusinki did not get a fair trial.

"This is medical evidence that was withheld. And it was deliberately withheld, because the person who called knew it had been deliberately withheld," she explained.

"Otherwise, why the anonymous phone call?" Moriarty noted.

"Why the anonymous call?" Zellner said. "They had inside information."

In June, Zellner filed a 67-page petition asking the trial judge to throw out the Melissa's conviction based on the new evidence.

"Do you think having these X-rays at trial might have made a difference?" Moriarty asked Zellner.

"It shows that it's a false confession. Because the entire case was based on there being a skull fracture," she replied. "...as the prosecution told the jury 32 times."

State's Attorney Nerheim now says he is reviewing Melissa's case to determine to whether the X-rays "had previously been given to the defense."

READ THE FULL STATEMENT: Lake County State's Attorney Michael G. Nerheim | June, 24, 2015

"I have been notified through media reports that counsel for defendant Melissa Calusinski has filed a document known as a Post-Conviction Petition.

This is a standard petition filed by defendants who have been convicted and sentenced for various criminal offenses.

As I have previously indicated, I am aware of no new evidence in this case that suggests that this defendant was improperly convicted of First Degree Murder.

In the future, should this defendant have any such evidence of actual innocence, I will review that claim as I would in any other case prosecuted by my office.

In the meantime, a Lake County jury unanimously found this defendant guilty for the First Degree Murder of an infant. An Illinois Appellate Court has affirmed that conviction. While we were not provided a courtesy copy by the defense, we will obtain a copy of the petition, review it, and respond accordingly."

But after Dr. Rudd saw the images, he changed the manner of Ben Kingan's death from "homicide" to "undetermined." Ben's death may have not been a murder at all.

"What is the chance, you think now, that Melissa Calusinski will get a new trial, at least have this conviction vacated?" Moriarty asked Zellner.

"I don't know when it will happen. But I feel extremely confident she will get a new trial," she replied. "We will never stop pursuing this case."

In September, the trial judge will decide whether to hold a new hearing that could be a first step to a new trial.

Newspaper reporter Ruth Fuller, who changed jobs because of this case, has been waiting a long time for this.

"I want to know what happened to Ben. That's what I want to know. And I think that we owe it to Ben to know what happened to him," she said.

Melissa's parents visit her often. They are confident they'll bring her home one day.