HOUSTON – A Texas inmate faces execution Thursday for the drug-related murders of four people more than 30 years ago.

Arthur Brown Jr. was convicted of the June 1992 deaths at a Houston home during a drug robbery. Authorities said Brown was part of a ring that transported drugs from Texas to Alabama and had bought drugs from Jose Tovar and his wife Rachel.

32-year-old Jose Tovar was killed during the drug robbery; his wife’s 17-year-old son, Frank Farias; 19-year-old Jessica Quiñones, the pregnant girlfriend of another son of Rachel Tovar; and 21-year-old neighbor Audrey Brown. All four were bound and shot in the head. Rachel Tovar and another person were also shot but survived.

“I don’t understand how someone could have just killed a pregnant woman and then made her suffer so much. It’s just beyond words,” said Maricella Quiñones, Jessica Quiñones’ older sister. Jessica Quiñones had been pregnant for 9 months and named her unborn daughter Alyssa.

One of Brown’s accomplices in the shooting, Marion Dudley, was executed in 2006. A third partner was sentenced to life in prison.

Brown, 52, who is from Tuscaloosa, Alabama, has long maintained that another person committed the murders.

His lawyers have asked the US Supreme Court to halt the execution, which was scheduled for Thursday evening at the state prison in Huntsville, Texas. They claim that Brown is intellectually disabled.

The Supreme Court has banned the death penalty for the developmentally disabled.

“MR. Brown’s intellectual limitations were known to friends and family. … Individuals who knew Mr. Brown during his lifetime have consistently described him as ‘slow,'” his lawyers wrote in the petition to the Supreme Court.

Brown’s lawyers have previously filed other appeals that have been rejected by lower courts. They have argued that he is innocent and that a witness actually implicated another suspect. They also claim that Brown’s conviction was tainted by racial bias, alleging that one of the jurors decided he was guilty because of his race. Brown is a black man.

A Houston judge on Tuesday denied a request by Brown’s lawyers for DNA testing of evidence they said could exonerate their client.

Josh Reiss, chief of the Post-Conviction Writs Division at the Harris County District Attorney’s Office in Houston, called Brown’s last-minute appeal a delaying tactic.

Reiss said school records submitted during Brown’s trial showed the inmate was initially believed to be intellectually disabled by third grade, by ninth grade that was no longer the case. Prosecutors also said Brown’s claims of innocence are problematic because the other suspect alleged to be the killer was found by investigators not to have been in Houston at the time.

“It was an absolutely brutal mass murder. … These families deserve justice,” Reiss said.

Maricella Quiñones, 52, said her sister was an innocent victim who was unaware the Tovars were sharing drugs from the home. She said her mother also blames the Tovars for what happened.

“My mother is not the same since my sister passed away,” said Maricella Quiñones.

Maricella Quiñones described her sister as a “very loving, caring person” who had been looking forward to becoming a mother. She said her family would likely never get closure.

– We lost two people. Alyssa never got a chance in life, she said.

Brown’s execution is the second of two in Texas this week. Another inmate, Gary Green, was executed Tuesday for fatally stabbing his estranged wife and drowning her 6-year-old daughter in a bathtub. Brown would be the fifth inmate in Texas and the ninth in the United States to be put to death this year.

Brown is one of six Texas death row inmates who are part of a lawsuit seeking to stop the state’s prison system from using what they say are expired and unsafe execution drugs. Despite a civil court judge in Austin agreeing with the claims for the time being, four of the inmates have been executed this year. ___ Follow Juan A. Lozano on Twitter at https://twitter.com/juanlozano70.