A spokesman for the UN high commissioner for human rights in Geneva said that the process to which Clayton Lockett was subjected on Tuesday may have amounted to "cruel, inhuman and degrading treatment" under international human rights law, and may have violated the US constitution.
Barack Obama admitted on Friday that the manner of Lockett's execution was "deeply troubling" and said he had asked the US attorney general, Eric Holder, to provide a review of the issues raised by it.
"I do think as a society we have to ask ourselves some difficult questions," he said.
A timeline published by the state of Oklahoma on Thursday showed that medical staff could not find a suitable vein on any of his limbs in which to inject the lethal drugs intended to kill him, and had to use his groin instead, which they covered, to prevent that area of his body from being seen by witnesses, The Gurdian reported.
The intravenous line into his groin failed, but the failure was not picked up for 21 minutes when the sheet was pulled back. The Guardian was among witnesses who watched as, for three minutes, Lockett fought against his restraints and attempted to speak, despite having been officially declared unconscious. When the IV failure was eventually discovered, it was found that the lethal drugs may not have entered Lockett correctly. "The drugs had either absorbed into tissue, leaked out or both," wrote the Oklahoma prisons director, Robert Patton in the timeline.
Lockett eventually died, apparently of a massive heart attack, one hour and 44 minutes after first being strapped to the gurney and ten minutes after the execution was officially called off. The state has refused to say whether, as required by its execution protocol, any attempts were then made to revive Lockett.
"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, spokesman for the UN high commissioner for human rights.
Colville said that the execution also appeared to run counter to the US constitution, which bars "cruel and unusual punishment". He told reporters: "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," referring to the case of Dennis McGuire, executed in Ohio in January with an allegedly untested combination of drugs.
"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," said Colville.
Of the 50 states in the US, 32 still have the death penalty in their laws, in addition to the US federal government and the military. Eighteen states have abolished the death penalty, most recently Maryland in 2013 and Connecticut in 2012. "The UN opposes the use of the death penalty in all circumstances," Colville said.