An autistic man whose murder conviction was based on a questionable diagnosis of "shaken baby syndrome" is to be executed in Texas on Thursday barring a last-minute stay from the US Supreme Court.
Robert Roberson, 57, is scheduled to die by lethal injection at the state penitentiary in Huntsville at 6:00 pm Central Time (2300 GMT) for the February 2002 death of his two-year-old daughter, Nikki.
Roberson is one of two death row inmates who are to be executed in the United States on Thursday.
Derrick Dearman, 36, is to be put to death by lethal injection in Alabama for the 2016 murders of five people who were related to his girlfriend.
Dearman confessed to the killings and has abandoned appeals against his death sentence.
Roberson, however, has asked the Supreme Court for a stay of execution.
Gretchen Sween, Roberson's attorney, said there is "overwhelming new medical and scientific evidence" that shows that the little girl died of "natural and accidental causes, not abuse."
The diagnosis of shaken baby syndrome, made at the hospital where Roberson's chronically ill daughter died, was erroneous and the cause of death was in fact pneumonia, which was aggravated when doctors prescribed improper medication, Sween said.
"The notion that Nikki's death was caused by abuse -- in the form of violent shaking and perhaps blunt impact -- was presumed based on prevailing medical beliefs at that time that have since proven to be devoid of scientific underpinning," Sween said in a petition to the Supreme Court.
The Texas Board of Pardons and Paroles declined by a 6-0 vote on Wednesday to recommend that Texas Governor Greg Abbott grant clemency to Roberson and commute his sentence to life in prison.
Abbott is unable to grant clemency without a recommendation from the board, but he can grant a 30-day reprieve of Roberson's death sentence.
"We pray that Governor Abbott does everything in his power to prevent the tragic, irreversible mistake of executing an innocent man," Sween said.
Roberson's case has drawn the attention of the Innocence Project, which works to reverse wrongful convictions, as well as best-selling American novelist John Grisham, Texas lawmakers and medical experts.
Also among those seeking to halt his execution is the man who put him behind bars -- Brian Wharton, the former chief detective in the town of Palestine.
"Knowing everything that I know now, I am firmly convinced that Robert is an innocent man," Wharton said at a recent press conference organized by Roberson's supporters.
Grisham, author of the legal thrillers "The Firm" and "A Time to Kill," also appeared at the event and said: "What's amazing about Robert's case is that there was no crime."
Roberson would be the first person executed in the United States based on a conviction of shaken baby syndrome, according to his lawyers.
Kate Judson of the Center for Integrity in Forensic Sciences said more than 30 parents and caregivers in 18 US states have been exonerated after being wrongfully convicted using "unscientific" shaken baby testimony.
Sween said Roberson's autism spectrum disorder, which was not diagnosed until 2018, contributed to his arrest and conviction.
"It is quite possible that Mr Roberson would not be on death row today, but for his autism," she said.
Sween said staff at the hospital where his daughter was admitted did not know he had autism and "judged his flat affect as a sign of guilt."
A bipartisan group of 86 Texas lawmakers had also urged clemency for Roberson, citing the "voluminous new scientific evidence" that casts doubt on his guilt.
There have been 19 executions in the United States this year.
