Texas is preparing to execute Ivan Cantu, a death row inmate who claims he’s innocent of the murders for which he’s to be put to death Wednesday evening, more than 20 years after his conviction.

Cantu’s execution could yet be halted or postponed, though a federal appeals court on Tuesday declined to stop the planned lethal injection or let the 50-year-old raise new challenges. The Texas Court of Criminal Appeals also rejected an appeal and a motion for a stay of execution.

Still, Cantu’s advocates – among them three jurors in the case – continue to call on the state’s Republican governor to give Cantu a 30-day reprieve, the most he could grant after the parole board’s unanimous rejection this week of the inmate’s clemency petition. His other advocates include reality star and entrepreneur Kim Kardashian, the actor Martin Sheen and anti-death penalty activist Sister Helen Prejean of “Dead Man Walking” fame.

The inmate’s staunchest supporter, though, may also be his first: His mother, Sylvia Cantu, remains convinced of her son’s innocence – and that his life will be spared – she told CNN on Tuesday.

“I’m still holding out hope that they press the pause button and they allow Ivan’s attorney to go in there and present the evidence that she has,” Sylvia Cantu said, “and hopefully, be able to exonerate him.”

In pressing for such a halt, Ivan Cantu has pointed to the cases of other Texas death row inmates – Rodney Reed and Melissa Lucio – who claim they also were wrongfully convicted. Indeed, at least 196 people sentenced to death in the United States since 1973 have been exonerated, 16 of them in Texas, according to the non-profit Death Penalty Information Center.

It’s unclear whether Cantu will ask the US Supreme Court to intervene, and CNN has reached out to his attorney. It’s not uncommon for death row inmates to turn to the high court to avoid execution, and sometimes those requests come at the last minute.

Now, Cantu hopes his execution is stopped so he can argue he was deprived of a fair trial and framed by those who, in his telling, are truly responsible for the 2000 killings of his cousin James Mosqueda and his cousin’s fiancée, Amy Kitchen, a nursing student.

Even so, Collin County District Attorney Greg Willis remains “fully convinced” of Cantu’s guilt, he said in a statement, citing the “undeniable evidence” featured at trial.

Prosecutor still ‘convinced’ of Cantu’s guilt

In court filings, Cantu and his attorney claim false testimony was presented at trial by the state’s key witnesses, including one who has since recanted. They also contend newly uncovered evidence supports an account Cantu told at the time of the killings, suggesting Mosqueda – an alleged drug dealer, per the inmate’s filings – was targeted and killed by rivals who also threatened Cantu over his cousin’s alleged debts. Cantu also has argued ineffective assistance of counsel, pointing in part to his trial attorneys’ decision to not call a single witness during the guilt-innocence phase of his trial.

Prosecutors, however, reject these claims, writing in their own court filings that Cantu’s arguments do nothing to “impugn the integrity of the guilty verdict.”

Cantu’s fingerprint was found on the magazine inside the gun used to kill Mosqueda and Kitchen, and DNA analysis showed blood on jeans found in Cantu’s trash can belonged to Mosqueda and Kitchen, according to prosecutors.

“It’s my firm belief that justice has been done in this case and that a Collin County jury’s verdict should be carried out on February 28th,” Willis said.

Cantu’s case was previously upheld on appeal. But he and his attorney say the evidence now supporting his innocence claim – much of it uncovered by podcaster Matt Duff – has not been heard by the courts.

Similar arguments were included in an appeal last April, shortly before Cantu was last scheduled to be executed. A judge subsequently withdrew Cantu’s execution date, but the Texas Court of Criminal Appeals ultimately dismissed Cantu’s request without considering the merits of the claims.

Jury foreman now sees ‘holes’ in the case

Collectively, the evidence has been enough to convince three of Cantu’s jurors to join the effort to halt Wednesday’s execution. They include the panel’s foreman, who now fears the jury was presented with an incomplete picture of the case, he told CNN.

“I’m convinced that there’s some holes in this,” Jeff Calhoun said, adding he took his responsibility as a juror very seriously.

Meanwhile, Cantu’s supporters have dedicated themselves to raising awareness about the case – a petition calling for a withdrawal of his execution date has garnered nearly 150,000 signatures – and to pressing GOP Gov. Greg Abbott to issue a reprieve.

“There are all these questions over the actual guilt of this man,” Prejean told CNN’s Jake Tapper this week, calling on people to contact Abbott on Cantu’s behalf. “He has one of the last vestiges of the divine right of kings. He’s a safety valve in all this. When justice is not done in the courts or you question it … he can grant a reprieve long enough to be able to look at the new evidence, which no court is yet willing to hear.”

Cantu asked in his clemency petition for a hearing and either a commutation to a life sentence or a 120-day reprieve.