UPDATE 1-Texas to execute man convicted of stabbing wife, stepsons to death in 2007

A man convicted of stabbing his wife and two stepsons to death and sexually assaulting his two stepdaughters in their home in 2007, telling them he believed his spouse was poisoning him, was due to be executed in Texas on Wednesday. Robert Sparks, 45, was scheduled to be put to death by lethal injection at 6 p.m. (2300 GMT) at the state's death chamber in Huntsville.

The U.S. Supreme Court denied a petition for a stay of execution about an hour before Sparks was scheduled to be put to death. A Dallas jury convicted Sparks of capital murder in 2008 in the slayings of his wife, Chare Agnew, and his two stepsons, Harold, 9, and Raekwon, 10.

Sparks was accused of stabbing Agnew 18 times while she slept in their Dallas home on Sept. 15, 2017, before waking the boys up, bringing them into the kitchen and stabbing them to death. Sparks then proceeded to wake up his two stepdaughters, LaKenya Agnew, 14, and Garysha Brown, 12. He tied them up and sexually assaulted them. He then told the girls that their mother tried to poison him, according to court documents.

Sparks locked his stepdaughters in a closet and left the home, stopping at his mother's house to borrow her car, and then his ex-girlfriend's home, where he told her he had killed his wife and two stepsons. He then called police and confessed, court records showed. After traveling to Austin for a few days, Sparks returned to Dallas and was arrested. He told police his wife had been poisoning him. He provided blood, hair and fingernail samples, as well as a cheek swab, to be tested for evidence of poisoning, but investigators were unable to find a lab capable of that type of test, according to court papers.

He had appealed his death sentence on the basis of his claim that a prosecution expert gave false testimony and that a courtroom bailiff may have tainted the jury's sentencing decision by wearing a homemade necktie depicting a syringe to show his support for capital punishment. In a statement "respecting" the high court's denial, Justice Sonia Sotomayor called the allegations about the bailiff's necktie "disturbing" but said insufficient evidence was found to conclude that jurors saw the tie.

Sparks would be the 16th inmate in the United States and the seventh in Texas to be executed in 2019, according to the Death Penalty Information Center. Texas has executed more prisoners than any other state since the Supreme Court reinstated capital punishment in 1976.