Texas is slated to put Robert Roberson III to death Thursday evening in what could be an unprecedented execution of a disabled man convicted of killing his daughter based on scrutinized science.

Roberson, 57, was sentenced to death in 2003 for reportedly fatally shaking his 2-year-old daughter, Nikki. He is scheduled to be executed by lethal injection about 6 p.m. in Huntsville.

If he’s put to death, Roberson, who is autistic, will become the first person in the country to be executed in a “shaken baby syndrome” case, according to lawmakers.

Roberson has maintained his innocence while on death row for more than two decades. His lawyers have made a slew of 11th-hour pleas to stop his execution, arguing the prosecution hinged on “junk science.” In a last-ditch effort late Wednesday, a Texas House committee subpoenaed Roberson to testify at a hearing about how a state law allowing people to challenge convictions with new science was applied in his case.

It was not immediately known if the subpoena would impact Roberson’s execution.

“It is not shocking that the criminal justice system failed Mr. Roberson so badly,” Gretchen Sween, one of Roberson’s attorneys, said in a statement sent to The Dallas Morning News. “What’s shocking is that, so far, the system has been unable to correct itself — when Texas lawmakers recognized the problem with wrongful convictions based on discredited ‘science’ over ten years ago.”

When Roberson found Nikki unresponsive in 2002, court documents say he rushed her blue, limp body to a Palestine hospital. Roberson said she fell from a bed, but medical staff suspected child abuse and called police because of her injuries, which included bruises on her face, a bump on the back of her head and bleeding outside her brain. Her cause of death was ruled to be blunt-force head injuries.

The case against Roberson — who had just become Nikki’s sole caretaker — relied on doctors’ testimony that her death was consistent with shaken baby syndrome, when an infant is severely injured from being violently shaken.

Brain bleeds were once believed to be one in a triad of symptoms used to diagnose shaken baby syndrome. In the decades since Roberson’s conviction, research has found those symptoms are not necessarily proof of abuse.

Just last week, the Texas Court of Criminal Appeals vacated the conviction of a Dallas County man accused of injuring a child because scientific advancements undermined shaken baby syndrome. More than 30 people who served time in prison after convictions involving the theory have been declared innocent, according to the National Registry of Exonerations.

Roberson’s lawyers have said new evidence shows Nikki, who was chronically ill, died of natural and accidental causes, including “severe, undiagnosed” pneumonia. According to court documents, she had a 104.5-degree fever days before she died; her medical history included chronic infections undeterred by multiple strains of antibiotics and “alarming breathing apnea spells.”

A coalition of bipartisan state lawmakers, bestselling author and Innocence Project board member John Grisham, and a former Palestine detective whose testimony helped convict Roberson, have denounced his impending execution.

The detective, Brian Wharton, said he believes Roberson is innocent. Despite earning Roberson’s forgiveness, Wharton has said he will be “forever haunted” by participating in his arrest and prosecution.

“We rushed to judgment,” Wharton wrote in a letter to the state’s parole board. “We were wrong, the jury was misinformed, and Robert is not guilty of any crime. If we are truly a nation of laws, a people who love justice in the most meaningful sense of that word, then Robert Leslie Roberson III must be set free.”

The parole board Wednesday did not recommend clemency to Roberson, who had petitioned for his death sentence be commuted or the execution delayed 180 days.

An Anderson County judge Tuesday rejected arguments from Roberson’s attorneys that his death warrant is illegitimate because the judge who oversaw post-conviction proceedings erred.

The state’s highest criminal appeals court has also repeatedly refused to intervene with Roberson’s death sentence.