A Texas man on death row because he killed a prison officer, blew kisses and yelled 'woof woof' to three female friends and two of his attorneys Wednesday before he was executed by lethal injection.

Travis Runnels, 46, was pronounced dead at 7.26pm at Huntsville prison north of Houston and became the 22nd person put to death in the US this year, minutes after a clemency appeal was rejected.

He never looked at the sister and brother-in-law of his victim, Stanley Wiley, as they watched through a window in an adjacent witness room.

Runnels responded 'No' when the warden asked if he had a final statement.

He mouthed words to the people watching through a window as he was belted to the death chamber gurney.

Runnels then took four short breaths and snored four times before he became lifeless.

Travis Runnels, 46, pleaded guilty in 2005 to the murder of prison supervisor, Stanley Wiley in 2003 and received the death sentence. He shouted 'woof, woof', took four short breaths and snored before he died by lethal injection Wednesday

It took 22 minutes for him to die after the dose of sedative pentobarbital.

Outside the Huntsville Unit prison, several hundred Texas corrections officers stood in formation, and Wiley´s sister, Margaret Robertson, hugged or shook the hands of many of them as she and her husband left the prison.

The execution was delayed about an hour until the U.S. Supreme Court turned down an appeal by Runnels' attorneys, who said a prosecution witness at his 2005 trial provided false testimony and that no defense was presented because his lawyers advised him to plead guilty and called no witnesses.

Janet Gilger-VanderZanden, one of his more recent attorneys, said Runnels changed during his 14 years on death row.

'There is true and authentic remorse for the death of Mr. Wiley. There are no excuses, rather there is a commitment to finding some kind of light in what was once a world of only darkness,' Gilger-VanderZanden said.

Lower courts and the Texas Board of Pardons and Paroles had also turned down Runnels' attorneys' requests to stop his execution.

He never looked at the sister and brother-in-law of his victim, who watched through a window in an adjacent witness room

In his clemency petition to the Texas Board of Pardons and Paroles, Runnels included letters from more than 25 individuals from around the world who said Runnels had worked to make amends for what he did.

'He has become a light that shines bright even in the darkest of spaces. The tragedy that he is responsible for will only be compounded if his valuable light were to be extinguished,' Kristin Procanick, from Syracuse, New York, wrote in one of the letters.

Runnels had received a 70-year jail sentence in 1997 for armed robbery.

In 2003, he slashed the throat of a prison supervisor, Stanley Wiley. Two years later he pleaded guilty to the killing and was sentenced to death.

At the prison shoe factory, Runnels approached Wiley from behind, pulled his head back and used enough force for the knife to go through his trachea and cut Wiley´s spinal cord.

It took 22 minutes for him to die after the dose of sedative pentobarbital

'It was cowardly,' prosecutor Randall Sims told jurors at Runnels' trial.

Wiley, who grew up in the Texas Panhandle city of Amarillo, began working as a state corrections officer in 1994. He was later promoted to a supervisory position.

Inmate Bud Williams Jr., who also worked at the shoe factory, testified that Wiley 'was a good guy'.

At his trial, Runnels´ lawyers didn't present any witnesses or evidence, including information about Runnels' troubled childhood and family history of drug and alcohol abuse, Gilger-VanderZanden said.

His lawyers later sought to have the penalty reversed. They said mitigating factors about his childhood were not introduced in the trial, and that an expert witness, A.P. Merillat, gave false testimony.

The lawyers accused Merillat of falsely telling a jury that if Runnels were given a life sentence instead of the death penalty, he would be free to roam through the prison and pose a danger to others.

Since 2010, the death sentences in two capital cases that also made use of Merillat's testimony have been reversed.

'Mr Runnels was sentenced to death based on the false "expert" testimony,' one of his lawyers said in their petition to the Supreme Court.

But Texas authorities argued that the jury would have sentenced Runnels to death without Merillat's testimony, because of his alleged record of violent attacks inside the prison.

The Texas Attorney General's Office pointed to assaults by Runnels on other guards after Wiley's death, including throwing feces and a light bulb at them, as evidence that he was a future danger and merited a death sentence.

'The evidence of Runnels' future dangerousness was overwhelming,' Texas lawyers told the country's highest court, which rejected Runnels' stay of execution request.

Executions have dropped in the United States as opposition to the death penalty has increased and due to legal questions over the methods of execution.

In 2016, the most recent low, 20 people were put to death, compared to 86 in 1999.

Four inmates who were convicted in the deaths of state correctional officers or other prison employees have been put to death since 1974, while three others remain on death row, according to Texas Department of Criminal Justice.