Missouri executed Michael Tisius on Tuesday evening, despite calls from legal, human rights and religious groups to call off the killing.

Tisius was executed by lethal injection as punishment for killing two jail guards when he was 19 years old, during a failed plot to help his former cellmate escape.

“Today marks another sad chapter of America’s perverse fascination with state-sanctioned homicide,” Tisius’ legal team wrote in a statement. “For many, it will be another example of how countries like Saudi Arabia, China and Iran are our few remaining peers internationally. But, for those of us who knew and loved Michael, it is a much sadder chapter. We watched the growth and maturity of a young man — who was neglected by his mother, abandoned by his father, and callously and viciously beaten by this brother — who learned how to form lasting, loving relationships. He learned how to trust. He learned how to value himself.

“We teach our preschoolers that two wrongs don’t make a right,” the lawyers continued. “Today, we watch our adults casually dismiss such eternal guidance. Michael dies in peace and in power. He expresses everlasting remorse to the families of Jason Action and Leon Egley. He has asked God for forgiveness as well.”

In the weeks leading up to his execution, the American Bar Association, the NAACP and representatives from the European Union and the Vatican asked Missouri Gov. Mike Parson (R) to grant him clemency. Six jurors from his trial, including two alternates, said they would either support or not oppose the governor using his clemency power to commute Tisius’ sentence to life in prison. Still, Parson declined to intervene.

Unlike some of the groups that urged Parson to grant clemency, the ABA does not support or oppose the death penalty. Instead, “it has a longstanding position that states should administer the death penalty only when performed in accordance with the constitutional principles of fairness and proportionality that limit the death penalty to the ‘worst of the worst’ offenders,” ABA President Deborah Enix-Ross wrote in a letter to Parson.

The ABA president noted Tisius’ young age and “neurological deficits” at the time of the crime, as well as the low flat fee of $10,000 paid to the lawyers who represented him at his second trial, as reasons why the death penalty was a “disproportionate” punishment.

As HuffPost previously reported, Tisius endured severe abuse, neglect and poverty throughout his childhood. In June 2000, when he was 19, Tisius served a 30-day probation violation sentence for theft in the Randolph County Jail. He shared a cell with an acquaintance named Roy Vance. Vance, 27 at the time and facing a 50-year sentence, convinced Tisius to help him escape after Tisius’ release.

Vance recognized Tisius could be “easily manipulated” and “took advantage of that,” he said in a recent video interview from prison. The plan was for Tisius to get a gun, return to the jail, order the guards into a cell and give the gun to Vance to take over. After he was released, Vance instructed his girlfriend Tracie Bulington to care for Tisius and not to let him out of sight, she said in her own video interview. She believed Vance was worried Tisius would back out.

Tisius appeared to “idolize” Vance, Bulington said. As the date of the planned escape attempt approached, Tisius spoke about Vance “kind of like a kid getting ready to go see his dad for the first time.”

When Tisius and Bulington made their way into the jail, Tisius panicked and shot and killed two jail guards, Leon Egley and Jason Acton. After initially fleeing, Tisius surrendered to the police and expressed immediate remorse. “I know what I have done was wrong and will never be fixed,” Tisius wrote in the statement after his arrest. “An Officer asked me if I could go back and do it all over what would I do. I said I would kill myself to save their lives.”

Vance and Bulington are each serving two life sentences.

During his 23 years of incarceration, Tisius was a prolific artist. He painted uplifting murals throughout the prison and donated his work to an auction to raise money for a domestic violence shelter. In the days before his death, he rushed to finish a painting with a motivational phrase on the wall of a rehabilitation unit for those in long-term segregation.

Missouri executes prisoners using pentobarbital, a drug often used to euthanize animals. Pharmaceutical companies have increasingly declined to supply drugs for use in executions, prompting corrections departments to turn to compounding pharmacies. Missouri’s Department of Corrections has refused to answer questions about how it obtained pentobarbital, what testing and safety measures are in place and when the drugs expire, the Kansas City Star reported earlier this week.

Autopsies of those who have been executed by lethal injection — including with pentobarbital — show signs of pulmonary edema, a condition in which the lungs fill with fluid and create the sensation of suffocating or drowning to death.