HOUSTON (AP) — A Texas man who could be the first person in the U.S. executed for a murder conviction tied to a diagnosis of shaken baby syndrome is facing a lethal injection Thursday evening amid assertions by his attorneys and a diverse coalition of supporters who say he’s innocent and was convicted on faulty scientific evidence.

Robert Roberson waited to hear whether his execution might be stopped by either Gov. Greg Abbott or the U.S. Supreme Court — his last two avenues for a stay. He is scheduled to receive a lethal injection at the state penitentiary in Huntsville.

Roberson, 57, was condemned for the 2002 killing of his 2-year-old daughter, Nikki Curtis, in the East Texas city of Palestine. Roberson has long proclaimed his innocence, backed by some notable Republican lawmakers and the lead detective on the case.

“He’s an innocent man and we’re very close to killing him for something he did not do,” said Brian Wharton, the lead detective with Palestine police who investigated Curtis’ death.

Roberson’s lawyers waited to see if Abbott would grant Roberson a one-time 30-day reprieve. It’s the only action Abbott can take in the case as the Texas Board of Pardons and Paroles on Wednesday denied Roberson’s clemency petition.

The board voted unanimously, 6-0, to not recommend that Roberson’s death sentence be commuted to life in prison or that his execution be delayed. All members of the board are appointed by the governor. The parole board has recommended clemency in a death row case only six times since the state resumed executions in 1982.

In his nearly 10 years as governor, Abbott has halted only one imminent execution, in 2018 when he spared the life of Thomas Whitaker, whose father had asked that his son not be put to death. The father had survived a shooting that Whitaker had masterminded.

“We pray that Governor Abbott does everything in his power to prevent the tragic, irreversible mistake of executing an innocent man,” Gretchen Sween, one of Roberson’s attorneys, said in a statement.

A spokesperson for Abbott did not immediately reply to an email seeking comment.

Roberson’s lawyers also have a stay request pending before the Supreme Court. The nation’s highest court has rarely granted 11th-hour reprieves to people on death row.

Late Wednesday, a Texas House committee that held an all-day meeting on Roberson’s case, issued a subpoena for him to testify at a hearing next week. It was not immediately known if the committee’s request could delay Thursday’s execution. A spokesperson for the Texas Department of Criminal Justice didn’t immediately reply to an email.

One of those who has been pushing to stop Roberson’s execution is Texas GOP megadonor and conservative activist Doug Deason, who has been speaking with Abbott’s staff.

“I believe he is innocent,” Deason wrote in a post on X on Tuesday.

During its meeting in Austin, the Texas House Criminal Jurisprudence Committee heard testimony about Roberson’s case and whether a 2013 law created to allow people in prison to challenge their convictions based on new scientific evidence was ignored in Roberson’s case.

Anderson County District Attorney Allyson Mitchell, whose office prosecuted Roberson, told the committee a court hearing was held in 2022 in which Roberson’s attorneys presented their new evidence to a judge, who rejected their claims. Mitchell said the prosecution’s case showed Curtis had been abused by her father.

“Based on the totality of the evidence, a murder took place here. Mr. Roberson took the life of his almost 3-year-old daughter,” Mitchell said.

Most of the members of the committee are part of a bipartisan group of more than 80 state lawmakers, including at least 30 Republicans, who had asked the parole board and Abbott to stop the execution.

Roberson’s scheduled execution has renewed debate over shaken baby syndrome, known in the medical community as abusive head trauma.

His lawyers as well as the Texas lawmakers, medical experts and others, including bestselling author John Grisham, say his conviction was based on faulty and now outdated scientific evidence. The diagnosis refers to a serious brain injury caused when a child’s head is hurt through shaking or some other violent impact, like being slammed against a wall or thrown on the floor.

Roberson’s supporters don’t deny head and other injuries from child abuse are real. But they say doctors misdiagnosed Curtis’ injuries as being related to shaken baby syndrome and that new evidence has shown the girl died from complications related to severe pneumonia.

Roberson’s attorneys say he was wrongly arrested and later convicted after taking his daughter to a hospital. They say she had fallen out of bed in Roberson’s home after being seriously ill for a week.

Roberson’s lawyers have also suggested his autism, which was undiagnosed at the time of his daughter’s death, was used against him as authorities became suspicious of him because of his lack of emotion over what had happened to her. Autism impacts how people communicate and interact with others.

The American Academy of Pediatrics, other medical organizations and prosecutors say the diagnosis of shaken baby syndrome is valid and that doctors look at all possible things, including any illnesses, when determining if injuries were attributable to it.

Roberson’s scheduled execution would come less than a month after Missouri put to death Marcellus Williams amid lingering questions about his guilt and whether his death sentence should have instead been commuted to life in prison. Williams was convicted in the 1998 killing of Lisha Gayle, a social worker and former St. Louis Post-Dispatch reporter.

Roberson’s execution is scheduled to take place on the same day Alabama is set to execute Derrick Dearman, condemned for killing five people with an ax and gun during a 2016 drug-fueled rampage.

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