By Lawrence Hurley
WASHINGTON (Reuters) - The U.S. Supreme Court on Tuesday declined to hear a death row inmate's challenge to Alabama's execution method, prompting liberal Justice Sonia Sotomayor to assert that the court should have considered whether the lethal injection procedures amounted to unconstitutional cruel and unusual punishment.
The court rejected an appeal by Thomas Arthur, convicted in the 1982 shooting death of his girlfriend's husband. In November, the court granted Arthur's request to put his execution on hold, but only because conservative Chief Justice John Roberts chose to side with the court's four liberals as a courtesy.
Sotomayor, in a strongly worded an 18-page opinion joined by fellow liberal Stephen Breyer dissenting from the court's refusal to hear the case, further exposed the rift among the eight justices over the death penalty.
"He has amassed significant evidence that Alabama's current lethal junction protocol will result in intolerable and needless agony," she wrote, referring to Arthur's argument that Alabama's lethal injection method violated the U.S. Constitution's Eighth Amendment ban on cruel and unusual punishment.
Arthur had proposed being executed by firing squad instead.
Sotomayor said American society's acceptance of different methods of execution has changed over time, as science reveals the level of suffering involved. States have cast aside hanging, electrocution and gas chambers for this reason, turning since the 1980s to an injection of lethal chemicals.
"What cruel irony that the method that appears most humane may turn out to be our most cruel experiment yet," Sotomayor wrote.
The justices have sharply disagreed among themselves over capital punishment. In 2015, they upheld Oklahoma's lethal injection process in a 5-4 ruling even as Breyer and fellow liberal justice Ruth Bader Ginsburg raised concerns about whether capital punishment violated the Eighth Amendment.
Breyer repeated his concerns on Dec. 12 on the same day the court rejected four other death penalty appeals. But the court has shown no signs it will take up the broader question of the constitutionality of the death penalty.
Arthur has been on death row for more than three decades since being convicted of fatally shooting Troy Wicker as he slept.
Lawyers for Arthur have said lower courts are divided over how to interpret the Supreme Court's 2015 Oklahoma decision. Their challenge focused on part of that ruling that said an inmate contesting a method of execution based on the risk of severe pain must show there is a "known and available alternative."
Arthur's lawyers asked the Supreme Court to clarify several issues, including whether prisoners can only pick available alternatives that are already available in the state where they are to be executed and whether, if they are proposing a lethal injection drug, they have to show the drug is readily available.
Under Alabama law, death by firing squad is not available, Sotomayor noted. As a result, the legal rule set by the Supreme Court in the 2015 case "permits states to immunize their methods of execution - no matter how cruel or how unusual - from judicial review and thus permits state law to subvert the federal constitution," she wrote.
Sotomayor said the meaning of the Eighth Amendment's prohibition on cruel and unusual punishment should be determined not by the standards that prevailed when the amendment was adopted in 1791 but instead by the evolving standards of decency that mark the progress of a maturing society.
The case focused on the use of a sedative called midazolam as part of the lethal injection drug cocktail. Sotomayor said examples are piling up with evidence of midazolam's inability to render an execution painless.
Sotomayor wrote, "Execution absent an adequate sedative thus produces a nightmarish death: The condemned prisoner is conscious but entirely paralyzed, unable to move or scream his agony, as he suffers what may well be the chemical equivalent of being burned at the stake."
(Reporting by Lawrence Hurley; Additional reporting by Andrew Chung; Editing by Will Dunham)