The Texas prisoner who is now days away from his execution has expressed his confidence that he will be granted clemency before the sentence is carried out.

Robert Roberson has been an inmate on death row for over 20 years, though potentially crucial questions are being asked as to the science that secured his conviction.

Roberson was found guilty of capital murder in the 2002 death of his two-year-old daughter, Nikki, who prosecutors and medical professionals claimed had died as a result of Shaken Baby Syndrome (SBS). The haunting title is attributed when a child suffers a serious brain injury, either through shaking or another type of violent impact.

Roberson, who was Nikki’s sole man­ag­ing con­ser­va­tor at the time of her death, professed his innocence, but was ultimately found guilty. The Texas Board of Parole last year voted not to recommend clemency, effectively green lighting his execution.

That execution has now been pencilled for Tuesday, October 16 amid a slew of doubts around the conviction, spearheaded by a podcast hosted by Lester Holt, who cast aspersions relating to Roberson’s actions having caused Shaken Baby Syndrome.

A clip from the podcast, titled The Last Appeal, was featured on Today, where Holt explained that the science behind SBS had been “undermined”.

“There is growing evidence that other things … can cause shaken baby, or the effects that [doctors] were talking about,” Holt said.

Roberson’s legal team are also arguing along the same lines, alleging that the conviction over Nikki’s death was secured on now-outdated scientific evidence.

The lawyers point to new evidence alleging that Nikki died as a result of complications related to severe pneumonia, as well as medication prescribed by doctors.

Gretchen Swen, one of Roberson’s attorneys, said on The Last Appeal: “The symptoms seen years ago as diagnostic of shaking are actually caused by a host of things.”

As per the Death Penalty Information Center, Swen said: “It’s shock­ing that we are dis­cov­er­ing the truth about this glar­ing, undis­closed evi­dence of bias only by chance, from a pod­cast, days before Robert is sched­uled to be exe­cut­ed for a tragedy that has been mis­la­beled as a crime.”

Podcast host Holt added: “The jury was never told that Nikki was a terribly ill child. She’d been seen by doctors more than 40 times in her short life, and in the days leading to her death Nikki had a 104.5 degree fever.”

Concerns over Roberson’s impending execution have also been shared by the former lead detective in the case of Nikki’s death, Brian Wharton.

Urging officials to grant Roberson clemency in a letter that’s contents were referenced by People, Wharton wrote: “I will be forever haunted by my participation in his arrest and prosecution. He is an innocent man.”

The man at the center of the storm, Roberson, has expressed hope that the truth of the matter will come to light before his sentence is carried out.

“It’s clear as day. They seen the evidence and they see that I really shouldn’t be here,” he said.