US author and winner of the literary prize John Grisham gestures as he poses on the red carpet before the screening of the film "Adrift" as part of the 44th Deauville US Film Festival in Deauville, north-western France on September 5, 2018. CHARLY TRIBALLEAU/AFP

WASHINGTON - Lawmakers in Texas, medical experts and the best-selling novelist John Grisham are pushing to save an autistic death row inmate whose daughter died in 2002 in a tragedy blamed on shaken baby syndrome.

Robert Roberson, 57, is scheduled to be executed on October 17 for the death of his two-year-old daughter Nikki in 2002.

Roberson took the girl to a hospital with severe head trauma and the child died the next day.

Lawyers for Roberson filed papers Tuesday with Texas Governor Greg Abbott and the Texas Board of Pardons and Paroles seeking clemency, or failing that, a 180-day stay of execution.

They argued that the diagnosis of shaken baby syndrome, made at the hospital where the child died, was erroneous.

In a letter to Texas officials, 34 doctors argued that the cause of death was in fact severe pneumonia, aggravated by the little girl's being prescribed the wrong medication.

The appeal also argues that Roberson's autism, which was not officially diagnosed until 2018, was misconstrued at the time as showing indifference to the death of the toddler and that this perception weighed heavily in his conviction.

"What's amazing about Robert's case is that there was no crime," Grisham, author of best-selling thrillers such as "The Firm" and "A Time to Kill," told a news conference. Grisham is a former lawyer who has been active in fighting cases of wrongful conviction.

"When you get into wrongful convictions you realize how many innocent people are in prison and how we could stop it, if we had the political gumption to do so. These cases really keep me awake at night," he said.

Roberson's attorney, Gretchen Sween, said "the state of Texas is preparing, in essence, to execute Forrest Gump." She was alluding to the gentle, mildly disabled character played by Tom Hanks in the 1994 film of the same name.

Sween argued that during the medical crisis involving his daughter, Roberson "shut down, and his external lack of affect was judged as a lack of caring."

Former police officer Brian Wharton, who led the investigation at the time, said the diagnosis of shaken baby syndrome "led the investigation from that point forward to the exclusion of all other possibilities."

"Knowing everything that I know now, I am firmly convinced that Robert is an innocent man," said Wharton, who is now a Methodist minister.

Wharton said that for the rest of his life he will regret his role in Roberson's arrest and prosecution.

Eighty-four Texas lawmakers signed a letter in support of the request for clemency for Roberson, more than a third of them Republicans.

These legislators said they are acting out of "grave concern that Texas may put him to death for a crime that did not occur, as new evidence suggests."

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© Agence France-Presse