What changed?

Last week, the state of Oklahoma executed Charles Warner after the Supreme Court refused to halt his execution while he appealed the constitutionality of the drugs used to kill him. Warner and three other death-row inmates argued that midazolam, a sedative used by Oklahoma and three other states in lethal injections, did not properly induce unconsciousness and would therefore lead to a horrifyingly painful death.

A five-justice majority, however, denied Warner's request for a stay without comment, and the state of Oklahoma executed Warner shortly thereafter. Justice Sonia Sotomayor and three other justices dissented, arguing that Warner and the other inmates had raised serious questions about Oklahoma's lethal-injection procedures. "I hope that our failure to act today does not portend our unwillingness to consider these questions," Sotomayor wrote.

Those hopes were not in vain. On Friday, the Supreme Court granted the three remaining plaintiffs' petition to hear their case, titled Glossip v. Gross, after it was relisted for further consideration. The justices gave no indication why they would refuse to stay Warner's execution, then agree to hear his case seven days later. Requests for the Court to stay the other three inmates' executions are forthcoming, said Dale Baich, one of their attorneys.

The Supreme Court has not addressed a lethal injection protocol's constitutionality since Baze v. Rees in 2008. A six-justice majority ruled then that a three-drug cocktail—the sedative sodium thiopental, the paralytic pancuronium bromide, and potassium chloride—did not violate the Eighth Amendment. But without sodium thiopental to anesthetize a condemned inmate, the court wrote, there would be "a substantial, constitutionally unacceptable risk of suffocation from the administration of pancuronium bromide and of pain from potassium chloride." In other words, the inmate would die in agony as he or she suffocated to death.

Amid intense pressure by anti-death-penalty activists, the last American drug maker to produce sodium thiopental withdrew from the market in 2011. State officials scrambled to find alternative sources in overseas markets, leading to a European Union embargo of lethal-injection drugs and raids by the U.S. Drug Enforcement Agency to seize stockpiles of sodium thiopental that had been imported without a license.

Without sodium thiopental, states then experimented with alternative cocktails. Midazolam, a sedative from the benzodiazepine family, was first used for executions in Florida as part of a three-drug cocktail without apparent complication. Outside of the Sunshine State, however, it has led to at least three botched executions. Last January, Dennis McGuire told observers during his execution with midazolam and hydromorphone in Ohio that he could "feel his whole body burning" as he died. In July, Joseph Wood gasped for air for one hour and fifty-seven minutes in Arizona during his executions with the same two-drug cocktail.

Oklahoma first used a three-drug midazolam cocktail identical to Florida's to execute Clayton Lockett last April. During his execution, an improper IV placement failed to deliver enough of the paralytic drug into his bloodstream, and he died of a massive heart attack while writhing in pain. In the aftermath, the other four Oklahoma death-row inmates appealed for a stay of their executions, arguing that midazolam did not produce a "deep, comalike unconsciousness" and was therefore an unacceptable substitute for sodium thiopental. As Justice Sotomayor observed last week, this paralytic's absence may have revealed pain and suffering that would otherwise be unobservable. This possibility raises serious questions about all executions performed with midazolam, including those carried out without incident in Florida.

The Supreme Court has never struck down an existing method of execution as unconstitutional. A ruling that forbids midazolam would reverberate even throughout states that do not use the sedative. No execution chamber in the U.S. currently uses the Baze cocktail, and no pharmaceutical company currently provides its key ingredient to American death rows. Even states like Texas, which uses a single-drug protocol with pentobarbital in its lethal injections, could find themselves on unsure constitutional footing.