An intellectually disabled man who killed three people at a convenience store in the US state of Missouri in 1994 has been executed despite pleas for clemency.
African-American man Ernest Lee Johnson, 61, was put to death by lethal injection for the murders of Mary Bratcher, Mabel Scruggs and Fred Jones during a botched robbery.
He was pronounced dead at 6.11pm local time, according to the Missouri Department of Corrections.
Efforts to save him by his lawyers and even the Vatican on the grounds that he was mentally impaired amounted to nothing.
Missouri's Republican Governor Mike Parson, on Monday rejected appeals to halt the execution, which took place in Bonne Terre, Missouri.
"The state is prepared to deliver justice and carry out the lawful sentence Mr. Johnson received," Parson said.
"The evidence showed Johnson went to great lengths to plan and conceal his crime," he said.
"Three juries have reviewed Johnson's case and recommended a sentence of death.
"Johnson's claim that he is not competent to be executed has been reviewed and rejected by a jury and the courts six different times, including a unanimous decision by the Missouri Supreme Court," the governor said.
In a final statement before his death, Johnson said he was sorry for what he had done and at peace.
"I am soory [sic] and have remorse for what I do," he said in the written statement.
"I want to say that I love my family and friends. I am thankful for all that my lawyer has done for me.
"They made me feel love as if I was family to them. I love them all, for all the people that has prayed for me I thank them from the bottom of my [heart].
"I love the Lord with all my heart and soul. If I am executed, I no [sic] where I am going to heaven.
"Because I ask Him to forgive me. God everyone. With respect, Ernest L Johnson."
Johnson's lawyers have repeatedly sought to block his execution on the grounds that he is intellectually disabled, arguing that would violate the Eighth Amendment of the US Constitution, which prohibits cruel and unusual punishment.
The Vatican's envoy to the United States sent a letter to the governor on behalf of Pope Francis last week urging him to halt the execution.
"This request is not based upon the facts and circumstances of his crimes; who could not argue that grave crimes such as his deserve grave punishments," said the Apostolic Nuncio, Archbishop Christophe Pierre.
"Nor is this request based solely upon Mr Johnson's doubtful intellectual capacity. Rather His Holiness wishes to place before you the simple fact of Johnson's humanity and the sacredness of all human life," he said.
In a filing with the US Supreme Court, Johnson's lawyers said he averaged scores of 67 on IQ tests, the range of intellectual disability.
They said his mother and a brother were intellectually disabled, and that he was born with fetal alcohol spectrum disorder.
"Johnson was held back twice in second and third grade because of his intellectual shortcomings," they said, and dropped out of school after a second attempt at ninth grade.
But the US high court on Tuesday denied Johnson's lawyers' motion for a stay of execution.
Two Democratic members of the House of Representatives from Missouri, Cori Bush and Emanuel Cleaver, also issued an appeal for clemency, saying Johnson's execution "would be a grave act of injustice".
"Killing those who lack the intellectual ability to conform their behaviour to the law is morally and legally unconscionable," they said.
"Like slavery and lynching did before it, the death penalty perpetuates cycles of trauma, violence and state-sanctioned murder in black and brown communities."
"This wasn't justice. This was cruelty," Bush tweeted after the execution was confirmed, and called to abolish the death penalty.