Problematic executions in Oklahoma and elsewhere have captured national headlines since early last year. Shown is the gurney in the the execution chamber at the Oklahoma State Penitentiary in McAlester, Okla. (Sue Ogrocki/AP)

The Supreme Court engaged in a bruising and at times fierce debate over the use of a lethal injection drug Wednesday, and the justices’ heated words seemed to reflect a deepening divide over the death penalty itself.

The justices were considering a challenge brought by death-row inmates in Oklahoma, who allege that the use of a sedative called midazolam has resulted in troubling executions that violate the Constitution’s prohibition on cruel and unusual punishment. Problematic executions in Oklahoma and elsewhere have captured national headlines since early last year.

On the court’s last day of oral arguments for the term, conservative and liberal justices were unusually antagonistic with the lawyers and with each other. The comments showed a deep distrust of the lawyers trying to delay executions using lethal injection and of state officials who minimize the risk of unconstitutional pain their procedures might cause.

“I mean, let’s be honest about what’s going on here,” said conservative Justice Samuel A. Alito Jr. “Executions could be carried out painlessly.”

The obstacle, he said, is that death-penalty opponents, who have been unable to persuade legislatures to do away with capital punishment or persuade the Supreme Court to find it unconstitutional, have pressured drug companies not to produce or sell the most effective drugs.

Bottles of the sedative midazolam are shown at a hospital pharmacy in Oklahoma City. (Uncredited/ASSOCIATED PRESS)

“Is it appropriate for the judiciary to countenance what amounts to a guerrilla war against the death penalty?” Alito asked.

On the other side of the ideological divide, Justice Sonia Sotomayor scolded Oklahoma Solicitor General Patrick R. Wyrick, saying that she would not believe anything he said “until I see . . . with my own eyes the context, okay?”

And Justice Elena Kagan said Oklahoma could not prove that its use of midazolam would render inmates properly unconscious so they would not feel the effects of the potassium chloride, which causes death — “being burned alive from the inside” as she described it.

“So suppose that we said, we’re going to burn you at the stake, but before we do, we’re going to use an anesthetic of completely unknown properties and unknown effects,” Kagan said to Wyrick. “Maybe you won’t feel it; maybe you will. We just can’t tell. And you think that that would be okay?”

The comments and lengthy, opinionated questioning led Chief Justice John G. Roberts Jr. to extend time to Wyrick and his opponent, Phoenix lawyer Robin C. Konrad.

“To an extent that’s unusual even in this court, you have been listening rather than talking,” Roberts said after Sotomayor grilled Wyrick at length about disputed expert testimony in the case. “And hopefully we’ll have a chance to hear what you have to say.”

The Supreme Court heard arguments on the constitutionality of the lethal injection procedure, a case that stemmed from a botched execution in Oklahoma. (Reuters)

The arguments came a year to the day after an execution in Oklahoma left an inmate writhing and grimacing on a gurney, drawing international attention to issues facing the lethal injection process in the United States.

The justices were revisiting the issue of lethal injection for the first time since 2008, when they upheld a three-drug combination and said it did not violate the Constitution’s ban on cruel and unusual punishment. At the time, these drugs were used across the country. But an ongoing shortage of lethal injection drugs, arising largely from European objections to capital punishment that interrupted the supply of drugs from Europe, has caused states to struggle to find new drugs, create different protocols and seek other methods.

In Oklahoma, when state officials could no longer obtain the drug they used to rely on, they turned to the drug midazolam. This particular drug was used in three problematic executions last year, turning it into a focal point for debates about lethal injections.

The most high-profile of these was Oklahoma’s bungled attempt to execute convicted murderer Clayton Lockett. He kicked, grimaced and survived for 43 minutes after the execution began. He eventually died after officials had already halted the process, and a state investigation blamed the bungled procedure on the manner in which the execution team inserted the needle.

Midazolam was also used last year in the execution of an Arizona inmate who gasped and snorted and took nearly two hours to die, as well as the lethal injection of an Ohio inmate who gasped and choked before dying after nearly half an hour.

So the court’s decision in the case could be a rather narrow review of whether a federal trial judge had made the right decision in authorizing the use of midazolam, which was approved by an appeals court.

But there are broader issues at work. And Wednesday’s testy exchanges among the justices indicate there could be lingering tension on the court over the manner in which the Oklahoma case was accepted.

The week before the case was taken, Oklahoma carried out its first execution since Lockett was put to death. The inmate, Charles Warner, who was convicted of raping and murdering an 11-month-old, had been set to die the same night as Lockett, but his execution was postponed.

The court’s four liberals wanted to stay that execution. But not one of the other justices would join them. Sotomayor wrote in a dissent that she found the idea that midazolam could “work as intended difficult to accept given recent experience with the use of this drug.”

But it takes only four justices to accept a case for oral argument, and that is what happened.

Conservative justices were clearly unhappy about revisiting the issue. After Konrad said it was the court’s duty to make sure executions did not violate the Eighth Amendment’s prohibition of cruel and unusual punishment, Roberts complained that anti-death penalty lawyers throw up roadblocks to executions but never offer what they would consider humane alternatives.

“The case comes to us in a posture where it’s recognized that your client is guilty of a capital offense, it’s recognized that your client is eligible for the death penalty, that that has been duly imposed,” Roberts said. “And yet you put us in a position with your argument that he can’t be executed, even though he satisfies all of those requirements.”

Justice Antonin Scalia expanded on that line of questioning. Konrad said it cannot be proved that midazolam is effective at producing a coma-like state in which an inmate would not be “jolted” awake by the introduction of the rest of the protocol: a paralytic drug and the heart-stopping potassium chloride.

“The reason it isn’t 100 percent sure is because the abolitionists have rendered it impossible to get the 100 percent sure drugs, and you think we should not view that as relevant to the decision that you’re putting before us?” Scalia asked.

Justice Anthony M. Kennedy, who might cast the deciding vote in the case, said Konrad’s answer was important to him.

“No. It’s not relevant,” Konrad answered. “The availability of another — .”

Sotomayor interrupted: “There are other ways to kill people, regrettably.”

“There are, Justice Sotomayor,” Konrad agreed.

“That are painless,” Sotomayor added.

Kagan and Alito, meanwhile, sparred about Kagan’s analogy about the pain caused by lethal injection being akin to being burned at the stake.

Konrad seemed wary of Alito’s hypothetical about whether it would be constitutional to burn someone at the stake if the person were properly anesthetized. Alito repeated:

“Burning somebody alive would not be a violation of the Eighth Amendment?”

Kagan didn’t wait for Konrad to answer.

“You see, but potassium chloride is burning somebody alive,” she said. “It’s just doing it through the use . . . of a drug.”

The case is Glossip v. Gross.