By Jonathan Allen

(Reuters) – Oklahoma intends to resume executions of condemned inmates using lethal injections after suspending capital punishment in 2015 following a series of botched executions, state officials said on Thursday.

The state had been developing a new execution protocol in which it would instead asphyxiate inmates using nitrogen gas, a plan Attorney General Mike Hunter unveiled in 2018.

But development of the new gassing protocol was taking too long and the state has since found a new supply of lethal drugs, Hunter said at a news conference in Oklahoma City alongside Governor Kevin Stitt.

“It is important that the state is implementing our death penalty law with a procedure that is humane and swift for those convicted of the most heinous of crimes,” said Stitt, a Republican.

Lawyers for death-row inmates said the announcement would revive their ongoing challenge to Oklahoma’s lethal injection protocol, which they say lacks transparency and breaches the U.S. Constitution’s ban on “cruel and unusual” punishment in its current form.

“Oklahoma’s history of mistakes and malfeasance reveals a culture of carelessness around executions that should give everyone pause,” Dale Baich, a federal defender representing some of the inmates, said in a statement.

Until 2015, Oklahoma had one of the busiest execution chambers in a country where a majority of states and the federal government allow capital punishment, a practice most countries have abolished.

The state’s executions stopped after serious errors. In 2014, an inmate convulsed and took more than 40 minutes to die after the state used an untested combination of three lethal drugs. In 2015, another inmate was executed using the wrong drug.

Oklahoma is returning to the same three-drug combination used in the botched 2014 execution, Hunter said, but has updated its protocol to include better training and oversight. The drugs are midazolam, a sedative; vecuronium bromide, a muscle relaxant; and potassium chloride, which stops the heart.

Hunter declined to say how the drugs were being obtained, citing state secrecy laws. He said development of the gassing method would continue in case lethal injection drugs again become unavailable.

The European Union bans the sale of drugs for use in executions, and pharmaceutical companies have refused to sell such drugs to U.S. prison systems. Several states have complained that they are no longer able to obtain the drugs.

There are 47 inmates on Oklahoma’s death row, Hunter said. A federal court ordered the state to give those inmates at least 150 days notice of a new protocol, and no execution dates have been set.

Death-penalty experts criticized the state for not changing the drugs it planned to use.

“No improvement in the protocol will address the fact that midazolam is an inappropriate drug to use in executions,” said Robert Dunham, director of the Death Penalty Information Center, a non-profit watchdog group. “Midazolam is not capable of knocking somebody out and keeping them insensate during the period in which other drugs are administered.”

(Reporting by Jonathan Allen; Editing by Chizu Nomiyama and Dan Grebler)