Austin, Texas - The Texas Supreme Court issued a last-minute stay of execution on Thursday to an autistic man whose murder conviction was based on what lawyers, doctors, and advocates say was a misdiagnosis of "shaken baby syndrome."

Robert Roberson had been scheduled to die by lethal injection at the state penitentiary in Huntsville on Thursday for the February 2002 death of his two-year-old daughter, Nikki.

But the Texas Supreme Court temporarily stayed the execution following an appeal from Texas lawmakers who issued a subpoena to Roberson so he can testify before a House committee that is examining his conviction.

"If the sentence is carried out, the witness obviously cannot appear," wrote Justice Evan Young.

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A bipartisan group of 86 Texas lawmakers has urged clemency for Roberson, citing "voluminous new scientific evidence" that casts doubt on his guilt, and the committee has subpoenaed him to testify on Monday.

Roberson has maintained his innocence and his attorney, Gretchen Sween, said there is "overwhelming new medical and scientific evidence" that shows his daughter 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, she said.

Roberson legal efforts had been rejected until the Texas Supreme Court decision.

The Texas Board of Pardons and Paroles declined by a 6-0 vote to recommend clemency to Roberson, and the US Supreme Court also rejected his request for a stay of execution, denying it without comment.

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.

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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.

Roberson would be the first person executed in the US 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."