The table in the execution chamber at the Oklahoma State Penitentiary in McAlester, Okla. (Sue Ogrocki/Associated Press)

The state of Oklahoma will use nitrogen gas to execute death row inmates going forward, officials said Wednesday, an unprecedented response to the inability of states nationwide to obtain lethal injection drugs.

Oklahoma has not carried out an execution in more than three years since high-profile mistakes involving lethal injections, including one that a grand jury described as an “inexcusable failure.”

The announcement by Oklahoma Attorney General Mike Hunter and Corrections Director Joe M. Allbaugh is still somewhat preliminary, as no execution protocol for using nitrogen gas has been created. Still, with states struggling to obtain lethal injection drugs, Oklahoma’s move is the latest in a series of dramatic efforts some officials have made to continue carrying out death sentences.

Oklahoma adopted nitrogen gas inhalation as its backup method of execution in April 2015 while the state was awaiting a U.S. Supreme Court ruling over the way lethal injections were carried out there. The court ultimately upheld Oklahoma’s lethal injection methods, but executions remained on hold as a grand jury investigated how officials wound up using the wrong drug to execute an inmate earlier that year.

Hunter’s office said that making nitrogen gas the state’s primary method of execution, rather than a backup, was a result of the state’s inability to obtain lethal injection drugs.

“Executions are the most profound application of state power,” Hunter said in a statement. “I believe in justice for victims and their families, and in capital punishment as appropriate for dealing with those whose commit these crimes. Using an inert gas will be effective, simple to administer, easy to obtain and requires no complex medical procedures.”

Dale A. Baich, one of the attorneys for 20 Oklahoma death-row prisoners challenging the state’s execution protocol, called on state officials to be “completely transparent” as it comes up with the new protocol.

“This method has never been used before and is experimental,” Baich said. “Oklahoma is once again asking us to trust it as officials ‘learn-on-the-job,’ through a new execution procedure and method. How can we trust Oklahoma to get this right when the state’s recent history reveals a culture of carelessness and mistakes in executions?”

Oklahoma’s last executions drew scrutiny in the state and nationwide. After the state executed Charles Warner in January 2015, officials acknowledged they had used the wrong drug for his lethal injection, an admission that came only after officials hastily called off another execution because they also had the wrong drug for it.

A grand jury investigation sharply assailed officials charged with carrying out Oklahoma’s executions, and Scott Pruitt, then the state’s attorney general, called them “careless, cavalier and in some circumstances dismissive of established procedures.” (Pruitt is now head of the U.S. Environmental Protection Agency.) Multiple prominent officials stepped down during the investigation into the drug mix-up.

In 2014, Oklahoma drew intense scrutiny for its death-penalty procedures after the execution of Clayton Lockett gained international attention. Lockett kicked, writhed and grimaced for 20 minutes before his execution was called off; he died of a heart attack not long after. An investigation found issues with the IV that was meant to deliver the fatal drugs.

Warner’s execution, which was scheduled to occur the same night as Lockett’s, was ultimately postponed until the following January. Oklahoma, which carried out at least one execution every year between 1995 and 2015 — one of only two states to do so, along with Texas — has not executed an inmate since then.

Oklahoma residents strongly backed a measure in 2016 that gave lawmakers the ability to adopt any constitutional method of execution, which Hunter, who replaced Pruitt, cited on Wednesday. He said state leaders had to “to utilize an effective and humane manner that satisfies both the Constitution and the court system.”

While use of the death penalty has dramatically declined nationwide, a handful of states have been outliers and continued to carry out executions. But in recent years, even those states dedicated to continuing the practice have run into roadblocks because of a shortage of lethal injection chemicals, driven in part by drugmakers’ objections to the death penalty.

In response to this shortage, states have turned to a variety of options, including adopting new drugs (Florida) or returning to older methods like the electric chair (Tennessee) and firing squad (Utah). Nevada and Nebraska also pushed recently to carry out the country’s first fentanyl-assisted executions, seizing on the powerful synthetic painkiller that has helped drive the opioid epidemic nationwide. Neither state has used the drug in a lethal injection so far.

Experts have said they know of no examples of states using nitrogen gas for executions. When nitrogen gas was approved as a backup method in Oklahoma, the corrections department said there was no protocol in place, and that remained the case Wednesday, nearly two years later. Allbaugh, the head of the corrections department, said his agency was working to develop a protocol.

“The victims of death row inmates have waited long enough for justice,” he said in a statement. “Trying to find alternative compounds or someone with prescribing authority willing to provide us with the drugs is becoming exceedingly difficult, and we will not attempt to obtain the drugs illegally.”

A financial analysis prepared for state legislatures before Oklahoma passed the nitrogen gas option in 2015 described the potential costs as “minimal” and said the process would require only a gas mask and a container of nitrogen.

This story was updated to include Baich’s statement.

Further reading:

Trump remains a staunch supporter of the death penalty, but many Americans are souring on it

Dylann Roof has been sentenced to death. Will the government ever be able to execute him?

The steady decline of America’s death rows

Fourth Arkansas execution in eight days prompts questions about inmate’s movements