More evidence emerged late this week about the gruesome execution of Clayton Lockett Tuesday night at the Oklahoma State Penitentiary in McAlester.

In a further indication of the brutality that prevails inside US prisons, it has now been officially confirmed that Lockett was tasered prior to the execution after refusing to leave his cell.

Lockett is the latest victim of what is being widely referred to, grotesquely, as a “botched” lethal injection. A cocktail of midazolam, veruconium bromide and potassium chloride was injected into a vein in Lockett’s groin beginning 51 minutes after he was strapped to the gurney in the execution chamber.

Within minutes after the injection Lockett began twitching violently and the curtains were drawn at this point to obstruct the view of the witnesses present. Witnesses said Lockett appeared to be enduring immense pain during the period when he remained visible. Even after being officially categorized as unconscious, Lockett continued trying to speak and struggled violently against the restraints.

Twenty-one minutes after the initial injection it was determined that the vein had collapsed and the injection failed. Oklahoma’s director of corrections Robert Patton wrote in a statement, “The drugs had either absorbed into tissue, leaked out or both.”

A faint heartbeat was detected, and the execution was called off at 6:56 pm. Lockett was then confirmed dead at 7:06 pm, 1 hour and 44 minutes after being strapped to the table. The official timeline provided by the prison contains no entry specifying what occurred during the 10 minutes prior to Lockett’s death.

According the Guardian, director Patton refused to answer questions about whether attempts were made to save or revive Lockett after the execution was cancelled, and Patton left the press conference immediately after being asked.

Lockett was effectively tortured to death, exposing once more the barbarism that reigns inside America’s criminal justice system and especially on its death rows. A study conducted by the Guardian found that between 1890 and 2010 fully 7 percent of lethal injections carried out in the US have been “botched,” leading to agonizing, hours-long execution sessions. In 2006, Angel Diaz spent half an hour writhing on the execution table after an injection missed his vein and was pronounced dead only after a second round of drugs was administered.

In the wake of Lockett’s death, the US is facing growing international condemnation for its aggressive policy of state execution. A statement released Friday by the office of the UN high commissioner for human rights said that the execution qualified as “cruel, inhuman and degrading.”

“The suffering of Clayton Lockett during his execution in Oklahoma on Tuesday, 29 April, may amount to cruel, inhuman and degrading treatment according to international human rights law,” said Rupert Colville, speaking on behalf of the UN high commissioner for human rights.

“The apparent cruelty involved in these recent executions simply reinforces the argument that authorities across the United States should impose an immediate moratorium on the use of the death penalty and work for abolition of this cruel and inhuman practice,” Colville said.

“The prolonged death of Clayton Lockett is the second case of apparent extreme suffering caused by malfunctioning lethal injections reported in 2014 in the United States,” said Colville.

US officials have responded by defending the widespread use of capital punishment. Asked during a press conference Friday about the execution, Obama reiterated his support for use of capital punishment, declaring, “The individual who was subject to the death penalty had committed heinous crimes, terrible crimes. And I’ve said in the past that there are certain circumstances in which a crime is - is so terrible that the application of the death penalty may be appropriate,” Obama said.

“I believe the legal process worked. I believe the death penalty is an appropriate response and punishment to those who commit heinous crimes against their fellow men and women,” Oklahoma Governor Mary Fallin said on Wednesday.

A study published Monday by the journal Proceedings National Academy of Sciences, “Rate of false conviction of criminal defendants who are sentenced to death,” showed that at least 4.1 percent of those sentenced to death in the US in the modern period have likely been innocent.

“We conclude that this [4.1 percent] is a conservative estimate of the proportion of false conviction among death sentences in the United States,” the study said.

The study also noted that “the rate of innocence must be higher for convicted capital defendants who are not sentenced to death than for those who are. The net result is that the great majority of innocent defendants who are convicted of capital murder in the United States are neither executed nor exonerated. They are sentenced, or resentenced to prison for life, and then forgotten.”

The state of Texas is currently preparing more executions by lethal injection, while fighting a court battle to maintain the shroud of secrecy over the chemical cocktails used by the state’s prison system. Robert Campbell is scheduled to be executed by Texas May 13.