The execution of Missouri death row inmate Herbert Smulls was temporarily halted by a U.S. Supreme Court order Tuesday after a last-minute plea by the defense argued that the state's refusal to disclose the source of the execution drugs could mean the inmate would be at risk of 'cruel and unusual punishment.'

Smulls' attorneys lodged a court motion saying that the state's refusal to disclose which compounding pharmacy they obtained the lethal injection drug pentobarbital from was a violation of the prisoner's First Amendment rights.

Further, they argued that execution by use of "lightly regulated" drugs threatened to subject the inmate "to cruel and unusual punishment."

State authorities have tried to obscure the identity of the compounding pharmacy that supplied the drug, going to such lengths as making the name of the business, like the execution team, protected from disclosure under Missouri law, the Guardian reports.

The Guardian continues:

Maya Foa, a leading campaigner for greater public access to information about death penalty drugs, said “there can be no way of guaranteeing that the execution will not amount to torture. This begs the question of what states are really trying to hide.”

The contention of Smulls's attorneys that secrecy combined with the relatively light regulation of compounding pharmacies could subject prisoners to drawn-out and potentially painful deaths through the use of weak or ineffective lethal drugs was underlined earlier this month in Oklahoma’s execution of Michael Wilson. The prisoner's final words as he was put to death by a massive overdose of pentobarbital, obtained from an unnamed Oklahoma compounding pharmacy, were: “I feel my whole body burning.”

The stay of execution also comes amidst uproar over the botched execution of Ohio inmate Dennis McGuire, during which an untested cocktail of "experimental" execution drugs left him struggling and gasping for air for over twenty minutes.

"Even if execution itself has not (yet) been found a violation of the U.S. Constitution’s ban on 'cruel' and unusual punishment, certainly a torturous death using experimental drug combinations is," Mike Brickner, Communications and Public Policy Director at the ACLU, wrote following McGuire's death.

The 56-year-old Smulls had been scheduled for lethal injection at 12:01 AM local time on Wednesday. Justice Samuel Alito reportedly signed the order, which was sent out Tuesday night.

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