Calls to spare the life of Texas death row inmate Robert Roberson are growing, with just over a day left before the state plans to execute him for the murder of his 2-year-old daughter – a crime Roberson’s advocates say did not happen.

If he’s put to death by lethal injection Thursday evening, Roberson’s attorneys say he would be the first person in the US executed based on a conviction that relied on an allegation of shaken baby syndrome – a misdiagnosis in Roberson’s case, they argue, and one they say has been discredited.

While child abuse pediatricians remain firm on the validity of the diagnosis, Roberson’s attorneys say there is ample evidence his daughter, Nikki Curtis, did not die of child abuse.

At the time of her death, she had double pneumonia that had progressed to sepsis, and she had been prescribed two medications now seen as inappropriate for children that would have further hindered her ability to breathe, they argue, citing medical experts. Additionally, she had fallen off a bed, and was particularly vulnerable in her sickly condition, Roberson’s attorneys say.

Other factors, too, contributed to his conviction, they argue. Doctors treating Nikki “presumed” abuse based on her symptoms and common thinking at the time of her death without exploring her recent medical history, the inmate’s attorneys claim. His behavior in the emergency room – viewed as uncaring by doctors, nurses and the police, who believed it a sign of his guilt – was actually a manifestation of autism spectrum disorder, which went undiagnosed until 2018.

“Very early on, Robert was the focus of everything to the exclusion of any other possibilities,” said Brian Wharton, the former Palestine, Texas, detective who led what he now believes was a too-narrowly focused investigation into Nikki’s death. He has since joined Roberson’s supporters in fighting to spare his life.

Roberson’s innocence claim underscores an inherent risk of capital punishment: a potentially innocent person could be put to death. At least 200 people – 18 in Texas – have been exonerated since 1973 after being convicted and sentenced to die, according to the Death Penalty Information Center.

As two of his latest appeals failed Tuesday, Roberson’s attorneys filed a request for a stay of execution with the US Supreme Court, arguing his due process rights were violated when the Texas Court of Criminal Appeals declined to consider additional evidence the inmate says would support his innocence claim. A separate appeal was also filed early this week with the Texas Court of Criminal Appeals, which on Friday denied another request to stay the execution.

Separately, Roberson’s attorneys have petitioned the Texas Board of Pardons and Paroles and GOP Gov. Greg Abbott for clemency, asking that this sentence be commuted to a lesser one, or that Roberson be granted a 180-day reprieve to allow time for his appeals to be argued in court.

The board is expected to issue its recommendation on clemency Wednesday. If it declines to recommend clemency, Abbott is limited to granting a one-time, 30-day reprieve.

State legislators voice support

In the meantime, Roberson’s many supporters are taking their own steps to call attention to his case in hopes of pressing the state into halting the execution.

The Texas Committee on Criminal Jurisprudence is holding a hearing Wednesday where it will hear testimony “related to capital punishment” and a Texas law – commonly referred to as the “junk science writ” – which opened a path for someone to challenge their conviction if there is new scientific evidence unavailable at the time of their trial.

While Roberson’s name is not mentioned in a notice about the hearing, his advocates say he should benefit from this law – and a member of the committee, Rep. Jeff Leach, a Republican from Collins County, told reporters Tuesday the hearing would “shine a light” on Roberson’s case “for all 31 million Texans to hear and watch and to see.”

“And we’re hopeful that by Thursday evening, we’re able to secure that pause button in this case,” said Leach, who supports the death penalty but has emerged as a key critic of its administration in cases featuring wrongful conviction claims.

The committee – made up of both Republicans and Democrats – has also urged the Texas Court of Criminal Appeals to halt the execution, citing the “junk science” law. Committee members want Roberson to be granted a stay while lawmakers consider amendments to the “junk science” law, they wrote in a letter brief filed before the court.

“It is beyond dispute that medical evidence presented at Mr. Roberson’s trial in 2003 is inconsistent with modern scientific principles,” the lawmakers wrote.

“We believe it would be a stain on the conscience of the State of Texas for an execution to proceed while efforts are underway to remedy deficiencies in how the law was applied to this case.”

A bipartisan group of more than 80 Texas legislators has supported Roberson’s case, and his request for clemency. Rep. Joe Moody, chair of the criminal jurisprudence committee, said on X last week the state needed to “pump the brakes before this stains Texas justice for generations.”

The author John Grisham – a board member of the Innocence Project, which has backed Roberson’s claim – also called for mercy Tuesday in an op-ed for the Washington Post.

“The evidence is assembled and available to the Texas authorities, but no one with the power to stop Roberson’s execution is paying attention,” Grisham wrote. “The courts slammed all the doors on the basis of technicalities, and even politicians’ pleas have been ignored.”

Diagnosis focus of courtroom debate

Roberson’s attorneys are not disputing babies can and do die from being shaken. But they contend more benign explanations, including illness, can mimic the symptoms of shaking, and those alternative explanations should be ruled out before a medical expert testifies with certainty that the cause of death was abuse.

Shaken baby syndrome is accepted as a valid diagnosis by the American Academy of Pediatrics and supported by child abuse pediatricians who spoke with CNN. The condition, first described in the mid-1970s, has for the past 15 or so years been considered a type of “abusive head trauma” – a broader term used to reflect actions other than shaking, like an impact to a child’s head.

Criminal defense lawyers also have oversimplified how doctors diagnose abusive head trauma, child abuse pediatricians say, noting many factors are considered to determine it.

“The conclusion is simply (Nikki) was a victim of abusive head trauma. Unequivocally,” Dr. Sandeep Narang, a child abuse pediatrician and a lawyer, told CNN after he said he was asked by a supporter of Roberson’s defense to review trial testimony in the case.

Still, the diagnosis has been the focus of debates in courtrooms across the country. Since 1992, courts in at least 17 states and the US Army have exonerated 32 people convicted in shaken baby syndrome cases, according to the National Registry of Exonerations.

Child abuse pediatricians like Dr. Antoinette Laskey, chair of the American Academy of Pediatrics’ Council on Child Abuse and Neglect, dispute these statistics. She pointed to a 2021 paper that found just 3% of all convictions in shaken baby syndrome cases between 2008 and 2018 were overturned, and only 1% of them were overturned because of medical evidence.

“I don’t know what to say about the legal controversy,” Laskey told CNN of the courtroom debate (She did not speak to Roberson’s case). “This is real, it affects children, it affects families … I want to help children; I don’t want to diagnose abuse: That’s a bad day.”

Last week, however, the Texas Court of Criminal Appeals ordered a new trial for a man sentenced to 35 years in prison for his conviction of injury to a child in a case that also relied on a shaken baby syndrome argument. In its argument, the court wrote “scientific knowledge has evolved regarding SBS.”

CNN’s Ed Lavandera, Ashley Killough, John Fritze and Sandee Lamotte contributed to this report.