Robert Pruett, 38, was executed in Huntsville, Texas Thursday night after maintaining his innocence to the bitter end.

Roughly an hour before dying by lethal injection, news broke that the U.S. Supreme Court had refused to halt his execution. Texas Gov. Greg Abbott did not give Pruett the 120 day reprieve requested by his defense team, and a six-member parole board voted Wednesday not to recommend clemency.

Pruett was convicted of killing Corrections Officer Daniel Nagle at a prison near San Antonio nearly 18 years ago. Nagle was stabbed with a metal rod, causing him to suffer a heart attack inside the facility, according to prosecutors and autopsy findings.

Pruett was the sixth prisoner Texas executed in 2017. But, even on Thursday, members of the public and national media outlets were coming to his defense.

Texas' "law of parties" first put Pruett behind bars with a 99 year sentence as a 16-year-old boy because he was present when his drug-addicted father stabbed a neighbor to death, and thus, he was considered an accomplice to the crime, according to a New York Times report in Pruett's defense. Four years into his sentence, Officer Nagle was murdered, and Pruett was convicted without any physical evidence.

According to the New York Times story, his conviction relied on the testimony of inmate witnesses who were offered deals to testify against Pruett. According to another report by Mother Jones, one of the key witnesses was told he would be transferred to a prison closer to his family if he testified against Pruett, and investigators threatened to charge him with Officer Nagle's murder if he didn't pin it on Pruett.

Social media erupted Thursday night, with critics slamming Gov. Abbott and the state of Texas for refusing to stop Pruett's execution. One activist posted video on Twitter of what he claimed were motorcyclists trying to drown out Pruett's last words.

>> Here is a link to the clemency petition filed on Pruett's behalf before he was put to death. <<

The Associated Press contributed to this report.