The ruling on the country's most commonly used methods of lethal injection cleared the way for executions across the United States.
The court adopted as a standard to determine the validity of an execution protocol whether it posed "substantial risk of harm," rejecting the inmates' plea that the standard be "unnecessary risk," SCOTUSblog.com reported.
In this case, "harm" would mean that the initial dose of sodium thiopental would not be administered properly, and the subsequent drugs that actually do the killing would cause significant pain.
Two men separately convicted of murder claimed the three drugs used in Kentucky's lethal injection process caused excruciating pain because there was at least some risk that the thiopental would not be properly administered, violating the Eighth Amendment of the Constitution. The method used in Kentucky is close to the protocols used by 36 states the federal government, SCOTUSblog.com said.
While the final vote was 7-2, no more than five justices signed on to any single opinion.
Chief Justice John Robert's plurality opinion said a death row inmate cannot successfully challenge an execution protocol "merely by showing a slightly or marginally safe alternative." Instead, the inmate must offer proof that options available present a "substantial risk of serious harm."
Justices Anthony Kennedy and Samuel Alito joined Robert's opinion. Alito filed a concurring opinion. Justices John Paul Stevens and Stephen Breyer each filed an opinion concurring in the judgment. Justices Antonin Scalia and Clarence Thomas filed concurring opinions, which other justices joined. Justices Ruth Bader Ginsburg and David Souter dissented.
Executions have been on hold since September pending the court's ruling.