Texas set to execute man on discredited 'shaken baby syndrome' hypothesis

Robert Roberson is set to be the first person to be executed in the U.S. based on the largely discredited "shaken baby syndrome" hypothesis unless Texas officials intervene.

Last week, Roberson's attorneys filed an emergency motion asking the Texas Court of Criminal Appeals to halt Roberson's Oct. 17 execution.

"[Roberson] fluctuates between despair, and then being buoyed with hope when anyone expresses sympathy and encouragement," his attorney Gretchen Sween told ABC News. "It is yet another layer of cruelty in this process watching what he's going through."

Nikki's death

According to Roberson's attorneys, he woke up to find his 2-year-old daughter Nikki lying on the floor at the foot of the bed one night in 2002. They say Roberson comforted her, put her back to bed and went back to sleep himself. He found Nikki unconscious with blue lips when he woke up the next morning. He took her to an emergency room, where she was ultimately pronounced dead.

Roberson, a 57-year-old man, was then convicted in her death.

Roberson was found guilty based on the testimony from a pediatrician who cited swelling and hemorrhages in Nikki's brain at the time as a "shaken baby syndrome" diagnosis even though there is limited evidence to support this as an accurate diagnosis. The hypothesis has come under serious scrutiny in biomechanical studies, as well as lengthening medical and legal literature. The medical examiner also suspected that Nikki sustained multiple head injuries, and considered the death a homicide in the official autopsy.

ABC News has reached out to both the pediatrician and medical examiner cited in court documents for comment.

Roberson is autistic, according to his legal team, which affects how he expresses emotions -- a concern that also arose during the trial.

Since his conviction, new evidence found that Nikki had pneumonia at the time of her death and had been prescribed respiratory-suppressing drugs by doctors in the days leading up to her death. These drugs include the narcotic drug codeine and promethazine, both of which are no longer prescribed to children Nikki's age or those in her condition because it could impair their ability to breathe and be deadly.

Following a post-mortem toxicology report, medical toxicology and emergency room medicine expert Dr. Keenan Bora concluded that high levels of promethazine are likely to have exacerbated Nikki's issues breathing.

A reexamination of her lung tissue by lung pathology expert Dr. Francis Green also found that chronic interstitial viral pneumonia and acute bacterial pneumonia were damaging her lungs, causing sepsis and then septic shock, leading to vital organ failure.

Over 30 medical and scientific experts have written to the Texas Board of Pardons and Paroles to reconsider Roberson's sentence that was hinged on the "shaken baby syndrome."

"Today, no reputable medical doctor would fail to conduct a thorough, multi-disciplined exploration of all possible causes of death because it is now known that many phenomena - including accidental short falls and naturally occurring disease - can cause the same intracranial conditions that 'mimic' inflicted head injury," the letter read.

Legal questions continue

Roberson's attorneys argue that state law Article 11.073 enables reviews of wrongful convictions based on changes in scientific evidence.

A bipartisan group of 86 Texas House of Representatives members have spoken out in support of Roberson's clemency request, arguing that Article 11.073 should have resulted in a new trial.

"Meeting Robert truly brought home the tragic reality of his situation," state Rep. Lacey Hull said in a statement to the advocacy group the Innocence Project. "Despite his pending execution, he is full of hope and faith and a desire to help others. He still grieves the loss of his daughter and is hopeful and thankful to everyone helping his cause. I am praying that he sees the justice and new trial that he and Nikki deserve."

In 2013, the Texas Court of Criminal Appeals denied Roberson's request to overturn his conviction, after a local judge argued his case had insufficient evidence, according to The Texas Tribune.

The Court of Criminal Appeals denied Roberson's most recent petition for a new trial in September, dismissing the application as "an abuse of the writ," or raising a claim that should have been raised in an earlier petition.

The court declined to address the merits of Roberson's claim in the dismissal.

Lead detective Brian Wharton, who directed Roberson to be arrested based on the "shaken baby" theory and testified against him in the trial, has also since called for Roberson's freedom.

"I will forever be haunted by the role I played in helping the State put this innocent man on death row," he said in a letter in support. "Robert's case will forever be a burden on my heart and soul. But it is not too late for Texas to change course and stop his execution. I sincerely hope that Governor Abbott and the Board will step in to do so."

Since 1992, more than 30 people have been exonerated after being wrongfully convicted under the shaken baby hypothesis, according to the National Registry of Exonerations.

ABC News has reached out to Texas Gov. Greg Abbott and the Texas Board of Pardons and Paroles for further comment.