John William King, who was white, received lethal injections for the slaying nearly 21 years ago of James Byrd Junior, who was chained to the back of a truck and dragged for nearly five kilometres along a secluded road in the woods outside Jasper, Texas.

The 49-year-old Byrd was alive for at least three kilometres before his body was ripped to pieces in the early morning hours of June 7, 1998.

Prosecutors said Byrd was targeted because he was black.

King was openly racist and had offensive tattoos on his body, including one of a black man with a noose around his neck hanging from a tree, according to authorities.

King, 44, was put to death at the state penitentiary in Huntsville, Texas. He was the fourth inmate executed this year in the US and the third in Texas, the nation's busiest capital punishment state.

The killing of Byrd was a hate crime that put a national spotlight on Jasper, a town of about 7600 residents near the Texas-Louisiana border that was branded with a racist stigma it has tried to shake off ever since.

King's lawyers had tried to stop his execution, arguing King's constitutional rights were violated because his trial lawyers didn't present his claims of innocence and conceded his guilt.

The US Supreme Court rejected King's last-minute appeal.

"From the time of indictment through his trial, Mr King maintained his absolute innocence, claiming that he had left his co-defendants and Mr Byrd sometime prior to his death and was not present at the scene of his murder.

"Mr King repeatedly expressed to defence counsel that he wanted to present his innocence claim at trial," A. Richard Ellis, one of King's lawyers, wrote in his petition to the Supreme Court.

The Texas Board of Pardons and Paroles also turned down King's request for either a commutation of his sentence or a 120-day reprieve.

Over the years, King had also suggested the brutal slaying was not a hate crime, but a drug deal gone bad involving his co-defendants.

King, who grew up in Jasper, was the second man executed for Byrd's killing. Lawrence Russell Brewer was executed in 2011. The third participant, Shawn Allen Berry, was sentenced to life in prison.

Louvon Byrd Harris, one of Byrd's sisters, said King's execution sent a "message to the world that when you do something horrible like that, that you have to pay the high penalty."

Compared to "all the suffering" her brother suffered before his death, Harris said King and Brewer got "an easy way out."

Mylinda Byrd Washington, another of Byrd's sisters, said she and her family will work through the Byrd Foundation for Racial Healing to ensure her brother's death continues to combat hate everywhere.

Australian Associated Press