Updated

As a 6 p.m. deadline looms, a Texas inmate set for execution Thursday is waiting for Gov. Greg Abbott to decide whether he will accept the state parole board’s rare clemency recommendation.

Thomas “Bart” Whitaker, 38, is scheduled for lethal injection for masterminding the fatal shooting of his mother, Tricia, and brother, Kevin, at their Houston home in 2003. His father, Kent, was also shot in the same attack but survived and led the effort to save his son from execution.

On Tuesday, the seven-member Texas Board of Pardons and Paroles unanimously recommended that Abbott commute Whitaker’s death sentence.

The Republican governor has fewer than 12 hours to accept the recommendation, reject it or do nothing. His office has not responded to inquiries about Whitaker’s case.

"The board only recommends," said Keith Hampton, one of Whitaker's attorneys. "The power resides purely in Gov. Abbott. He could do nothing, which would be pretty amazing. He could literally do nothing. Then (Whitaker) gets executed."

If Abbott rejects the recommendation, Whitaker will be one of three executions scheduled for Thursday.

Florida and Alabama also have executions set for Thursday night and if they are carried out, it would mark the first time in more than eight years that three convicted killers were put to death in the U.S. on the same day.

The other prisoners set to die Thursday are Doyle Lee Hamm in Alabama and Eric Scott Branch in Florida.

In Texas, 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 Dec. 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 fatally shot. Kent Whitaker and Bart were wounded.

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Kent Whitaker speaks to reporters after asking the chairman of the Texas Board of Pardons and Paroles to spare the life of his son Thomas Whitaker, a death row inmate who is set the be executed Feb. 22. (REUTERS)

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.

"I'm 100 percent guilty," Whitaker testified at his trial in 2007. "I put the plan in motion."

In the clemency petition, Whitaker's attorneys said his execution would "permanently compound" his father's suffering and grief, and compared the case to the biblical story of Cain and Abel, where God sent Cain to "restlessly wander" after killing his brother.

It's 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-Gov. 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.

The U.S. Supreme Court, which last year refused to review appeals in Whitaker's case, also could 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.

The Associated Press contributed to this report.