In an effort to at least stall his execution, Hooper had sued the state last month claiming Oklahoma's three-drug lethal injection protocol was unconstitutional. The lawsuit sought to force the state to have an extra dose of pentobarbital, a sedative, on hand during his execution.
Pentobarbital is the first drug administered and is used to render a condemned inmate unconscious. It's followed by vecuronium bromide, which stops the inmate's breathing, then potassium chloride to stop the heart.
Hooper's attorney, Jim Drummond, had argued that if the sedative were ineffective, the remaining drugs could cause great pain in violation of the Eighth Amendment's prohibition against cruel and unusual punishment. The lawsuit also noted that other states have adopted a one-drug process using a fast-acting barbiturate that supporters say causes no pain.
But the claims were rejected by a federal judge, then upheld by a federal appeals court. And the U.S. Supreme Court rejected Hooper's request without elaboration earlier Tuesday.
Hooper was the fourth death-row inmate executed in Oklahoma this year. Gary Roland Welch was executed Jan. 5 for fatally stabbing a 35-year-old man, and Timothy Stemple was executed on March 15 for the beating death of his wife. Michael Selsor was put to death on May 1 for the shooting death of a Tulsa convenience store manager.