A 61-year-old African-American man was executed Tuesday in the U.S. state of Missouri, despite pleas for clemency from the Vatican and his lawyers on the grounds that he was intellectually disabled.

Ernest Lee Johnson was put to death by lethal injection for the 1994 murders of three convenience store workers during a botched robbery in Columbia, Missouri.

He was pronounced dead at 6:11 pm (2311 GMT), according to a statement from the Missouri Department of Corrections.

Missouri Governor Mike Parson, a Republican, on Monday had 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 in a statement.

“The evidence showed Mr. Johnson went to great lengths to plan and conceal his crime,” he said. “Three juries have reviewed Mr. Johnson’s case and recommended a sentence of death.

“Mr. 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.

Johnson’s lawyers repeatedly have sought to block his execution on the grounds that he is intellectually disabled, arguing that would violate the Eighth Amendment of the Constitution, which prohibits cruel and unusual punishment.

Vatican request

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 Mr. Johnson’s humanity and the sacredness of all human life,” he said.

In a filing with the U.S. Supreme Court, Johnson's attorneys 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 Johnson was born with fetal alcohol spectrum disorder.

“Mr. 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 U.S. high court Tuesday denied Johnson’s attorneys’ motion for a stay of execution.

‘Grave act of injustice’

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 behavior to the law is morally and legally unconscionable,” they said in a statement.

“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.

Johnson was convicted of killing three convenience store employees – Mary Bratcher, Mabel Scruggs and Fred Jones – while robbing the store to get money to buy drugs. (AFP)

Update news