A Texas inmate set for execution on Thursday evening is waiting to hear if a rare clemency recommendation to spare his life at the urging of his father will be accepted.

Thomas “Bart” Whitaker, 38, is scheduled for lethal injection for masterminding the fatal shootings of his mother and brother at their suburban Houston home in 2003 in a plot to collect inheritance.

Whitaker’s father, Kent, was also shot in the same attack but survived and has led the effort to save his son from execution.

The seven-member Texas Board of Pardons and Paroles, whose members are appointed by the state’s governor Greg Abbott, recommended unanimously on Tuesday that Mr Abbott commute Whitaker’s death sentence.

Mr Abbott could accept the recommendation, reject it or do nothing. His office did not respond on Wednesday to inquiries about the Whitaker case.

“The board only recommends,” said Keith Hampton, one of Whitaker’s lawyers. “The power resides purely in governor Abbott. He could do nothing, which would be pretty amazing. He could literally do nothing. Then (Whitaker) gets executed.”

State law language does not specify the governor “must” act, another of Whitaker’s lawyers, James Rytting, said.

It is only the fourth time since the state resumed executions in 1982 that the parole board has recommended clemency within days of an inmate’s scheduled execution.

In the previous cases, then-governor Rick Perry accepted the board’s decision in one case and rejected the other two, who subsequently were put to death in the nation’s most active capital punishment state.

Prosecutors in Fort Bend County, where the killings occurred at the Whitaker home in Sugar Land, just south-west of Houston, criticised the parole board recommendation. If Mr Abbott agreed to the board’s clemency recommendation, “then it’s a total injustice, absolute injustice on this,” said Fred Felcman, one of the trial prosecutors.

The US Supreme Court, which last year refused to review appeals in Whitaker’s case, could also weigh in at the last minute.

Whitaker and another Texas death row inmate are plaintiffs in an appeal pending before the high court questioning whether Texas’ use of a compounded version of the powerful sedative pentobarbital for executions would cause unconstitutional pain. The case had been scheduled for the justices’ conference on Friday, the day after Whitaker could be executed.

State attorneys were opposing the request to block the execution, saying claims about the drug’s ineffectiveness had been repeatedly rejected in the courts.

Kent and Patricia Whitaker and their two boys had returned home the night of December 10, 2003, following a restaurant dinner to celebrate Bart Whitaker’s college graduation when they were confronted by a gunman wearing dark clothes and a ski mask. Patricia Whitaker and her 19-year-old son, Kevin, were shot dead. Kent Whitaker and Bart were wounded.

Nearly two years later, Bart Whitaker was arrested in Mexico after investigators determined he arranged the plot in hopes of collecting a family estate he believed was worth more than 1 million US dollars.

“I’m 100% guilty,” Whitaker said at his trial in 2007. “I put the plan in motion.”

He hated his parents and brother at the time, he said.

Whitaker’s father said he loves and has forgiven his son, calling him a changed person.

“As the greatest victim in this case, you don’t have to convince me how awful this crime was,” Kent Whitaker said.

Evidence showed the murder plot included two of his friends and was at least his third attempt to kill his family. As part of the scheme, Whitaker’s wound to his arm was meant to draw attention away from his involvement. Unknown to his parents, the dinner celebration marking his graduation was a fraud. He had dropped out of school months earlier.

The gunman, Chris Brashear, pleaded guilty in 2007 to a murder charge and is serving life in prison. Another man, Steve Champagne, who drove Brashear from the Whitaker house the night of the shootings, took a 15-year prison term in exchange for giving evidence at Whitaker’s trial.

AP