An undated Arizona Department of Corrections handout showing Joseph Rudolph Wood. (Arizona Department Of Correction / Handout/EPA)

For the third time this year, an execution in the United States went awry, prompting outrage, questions and calls to get rid of the death penalty. But yet again, experts said it was unlikely that the episode would lead to widespread changes or prompt states to seriously alter their policies.

The execution of Joseph R. Wood III, who was killed by lethal injection Wednesday in Arizona, took nearly two hours. Witnesses reported that Wood was gasping and struggling to breathe, although state officials and other witnesses argued that he was only snoring. But the amount of time it took Wood to die, which lasted for so long that his attorneys were able to file requests asking for a stay while the execution was ongoing, prompted Gov. Jan Brewer (R) to order a review.

“Any time there’s a significant event like this one, it carries some weight,” said Deborah W. Denno, a Fordham University professor and expert on the death penalty.

In particular, she said, Wood’s prolonged death could increase scrutiny of how states use the sedative midazolam in executions. That drug was used, along with hydromorphone, during the execution at the Arizona State Prison Complex an hour outside of Phoenix. Wood’s attorneys had argued that more information was needed about these two drugs, which were combined for the first time in an execution in Arizona.

The state altered its lethal injection protocols to use these two drugs because the ongoing shortage of lethal injection drugs left it unable to find pentobarbital.

“Neither of these drugs are designed to kill,” said Joel Zivot, an assistant professor of anesthesiology at the Emory University School of Medicine. “Companies create and sell phamaceuticals where their purpose is to heal. The state takes these pharmaceuticals and tries to imagine a different purpose for them, and to see if they can turn these medicines into poisons.”

Midazolam also factored into two other episodes this year that provoked concern. In Ohio, witnesses said Dennis McGuire repeatedly gasped during his January execution, which lasted for almost half an hour.

And a botched execution in Oklahoma drew worldwide attention in April, with witnesses reporting that Clayton Lockett was grimacing and clenching his teeth before the execution was called off. Lockett died a short time later, and an independent autopsy pointed to problems with the IV placement, rather than the drugs used.

The drawn-out execution in Arizona renewed calls for the United States to do away with capital punishment.

“Capital punishment is cruel, inhuman and degrading, and the distressing case of Joseph R. Wood III’s potentially botched execution in Arizona is only the latest example of why this abhorrent practice must be abolished in the United States,” Steven W. Hawkins, executive director of Amnesty International USA, said in a statement.

But officials in states that conduct the most executions said they did not plan to change how they carry out the death penalty. Missouri said it is still prepared to hold its seventh execution of the year on Aug. 6 using the same drug protocol — an injection of pentobarbital — it has used since last year. That would tie it with Florida and Texas for the most executions so far this year.

The Texas Department of Criminal Justice said that it would continue to use a single dose of pentobarbital, spokesman Robert C. Hurst said in a statement. “The agency has used this protocol since 2012 and has carried out 33 executions without complication,” he said. ​

See a breakdown of the 1,379 people —responsible for killing more than 2,074 — who have been put to death in the U.S. since the Supreme Court reinstated the death penalty in 1976.

A spokeswoman for the Ohio Department of Corrections said that the state is always evaluating its policies but declined to comment further because there is a pending lawsuit against Ohio by McGuire’s family.

On Thursday, Dale Baich, an attorney for Wood, called for an independent investigation into the execution. While Brewer has ordered the state Department of Corrections to conduct a review, Baich argued that an outside inquiry is needed to find out much more about the drugs that were used “following an execution cloaked in secrecy that went wrong.”

Wood’s attorneys had filed a request for an emergency stay of execution an hour into the procedure, saying that Wood remained alive and was gasping. They also filed a stay request with Supreme Court Justice Anthony M. Kennedy, who is the justice assigned to hear emergency requests from the West. Supreme Court personnel said it was extremely rare for a justice to receive a request to stop an execution already underway and were unable to recall a similar instance.

Wood’s attorneys filed the stay request with the Supreme Court at 6:27 p.m. Eastern time. The clerk’s office informed the lawyers at 6:46 p.m. that Kennedy had denied the stay, three minutes before Wood was pronounced dead.

Executions are, by nature, carried out far from public view, witnessed by a handful of individuals in small rooms inside prison complexes. Many occur without much notice. It often takes a gruesome episode to capture public attention.

The prevalence of the death penalty, meantime, is in decline. A third of the 18 states to abolish the practice have done so since 2007. The number of executions has also dropped, with the average number of executions falling significantly after a surge in executions in about 2000.

“The death penalty has become less relevant,” Richard Dieter, executive director of the Death Penalty Information Center, said in an interview after the Ohio episode. “For most of the country, it’s just not used enough to be a regular part of the criminal justice system.”

Meanwhile, even as a majority of Americans still support the death penalty, the percentage of Americans in favor of it dropped from 78 percent in 1996 to 55 percent last year, the Pew Research Center reported.

“I like to say that support for the death penalty is wide but shallow,” said Douglas A. Berman, a professor at Ohio State University and an expert on sentencing and the death penalty. “By that I mean, people are comfortable with the death penalty when it seems to be functioning well.”

People seem to want this ultimate punishment to be available while simultaneously looking to avoid any brutality, he said.

“There’s a kind of . . . dichotomy or cognitive dissonance to trying to make both of those things operate,” he said. “It’s based in a residual humanity that we retain even as we want to condemn the most brutal of crimes.”

Robert Barnes contributed to this article.