"Gov. Abbott has the power to stop the spectacle of prison guards leading a blind, mentally incompetent delusional man to the death chamber," attorney Maurie Levin said, according to The Associated Press.
Thomas, who started hearing voices when he was nine years old and first attempted suicide when he was ten, fatally stabbed his 20-year-old estranged wife, Laura Christine Boren, their four-year-old son Andre Lee and her 13-month-old daughter Lehya Marie Hughes in 2004 in Sherman, Texas. He also cut out the hearts of the two children and later told police that God had instructed him to commit the killings and that he believed all three were demons.
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Thomas was sentenced to death for killing the little girl after jurors rejected his insanity defense, and prosecutors argued that he knew his actions were wrong and exacerbated his mental condition with drug use.
Thomas has spent the last 15 years at a unit for the state's most mentally ill prisoners, located south of Houston. He has – since the killings – gouged out his eyes. His attorneys said he ate one of his eyes to ensure that the government could not hear his thoughts.
Authorities say that Thomas' victims and their families should not be forgotten and that, if he is found competent, the execution should go forward.
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"A jury has spoken about what justice should be in this case. We are not going to ignore that," J. Kerye Ashmore, of the Grayson County District Attorney’s Office, said, according to The AP.
Thomas' attorneys have said his trial was problematic, because jurors who said they opposed interracial marriage were allowed to serve. Thomas is Black, and his estranged wife was White.
His attorneys will have to file a court motion asking that his competency be reviewed, but a judge would ultimately decide the issue.
Abbott has granted clemency to only one death row inmate since taking office in 2015.
The Associated Press contributed to this report.