A group of 10 Arkansas death row inmates has challenged a new law authorizing their execution by nitrogen gas, arguing the law is unconstitutional because it violates the state's separation of powers doctrine, an attorney confirmed to Law360.

The prisoners, all of whom were sentenced to die by lethal injection, argued in a suit filed Tuesday that the law gives state officials "unfettered discretion" to choose the execution method, while offering no guidance on how to use the lethal gas.

The suit, which asks the court to declare the law unconstitutional and to bar the state from executing the prisoners using nitrogen gas, also argues the law violates the power of the courts by modifying existing death sentences.

"This law delegates unprecedented and unchecked authority to unelected executive branch officials in the Division of Correction, who are now empowered to gas our clients to death despite the fact that all of them were sentenced under a law that only allowed for execution by lethal injection," said Heather Fraley, a federal public defender and attorney for several of the plaintiffs, in a statement issued Tuesday after the complaint was filed in a state trial court in Little Rock, Arkansas.

Since 1983, when it ditched electrocution, Arkansas has punished people convicted of capital murder by executing them with lethal injection or sentencing them to life in prison without the possibility of parole.

Act 302, which passed during the most recent legislative session and went into effect on Tuesday, adds nitrogen hypoxia — suffocation with nitrogen gas — as an authorized method of execution alongside lethal injection. Under the statute, state officials are also allowed to choose between a single-dose or multidrug protocol in lethal injections

The law adds Arkansas to the group of states — which include Alabama, Louisiana, Mississippi and Oklahoma — that specifically authorizes nitrogen gas executions. Arizona, California and Wyoming allow killing prisoners using lethal gas, without specifying which chemical can be used.

In a call with Law360 on Tuesday, Fraley clarified that the suit doesn't challenge the execution method itself, but what she described as an unconstitutional delegation of power to state officials to choose the procedure to execute prisoners and impose a different punishment than the one juries originally selected for the 10 prisoners.

"We just don't know what the jury's sentencing calculus may have been if nitrogen had been an available method of execution," Fraley said. "The statute creates more questions than it does answers when it comes to a nitrogen execution."

Last year, Alabama was the first jurisdiction in the world to execute a person — Kenneth Eugene Smith — by using nitrogen gas suffocation.

Witnesses to the Jan. 25, 2024, execution, which lasted approximately 28 minutes, said that Smith convulsed on the gurney and gasped for air as he breathed in the nitrogen gas — which is odorless and colorless — through a mask.

On March 18, Louisiana became the second state to execute a prisoner — Jessie Hoffman Jr. — using nitrogen hypoxia, as other states are turning to alternative methods amid legal and practical challenges to lethal injection.

Only Alabama and Louisiana have so far issued protocols for nitrogen gas use, according to the Death Penalty Information Center. Arkansas has not carried out an execution since 2017. The last death sentence imposed in the state was in 2018.

While emphasizing that the suit filed Tuesday focuses on the state Legislature's alleged overreach in the new law, Fraley said that the nature of nitrogen gas hypoxia itself deserves attention.

"We have seen in states like Alabama that gas executions are gruesome and horrifying," she said. "We hope they will never happen in Arkansas."

The 10 prisoners housed inside the Varner Unit near Grady, Arkansas, said in the complaint that their respective juries were explicitly instructed by judges to choose between "death by lethal injection" and life without parole, arguing that the law usurps the power of the judiciary to impose punishment.

The plaintiffs argued that the law violates the separation of powers spelled out in Article IV of the Arkansas Constitution by delegating to the Arkansas Division of Correction — which is part of the state's Department of Corrections — the power to determine the method and means of execution without providing any specific guidance.

"By leaving the decision as to how the state will carry out executions to the ADC, with no guidance as to how to make that decision, the legislative branch grants excessive discretion to the executive branch," the complaint says.

Legal challenges to earlier statutes determining execution methods have failed.

Some of the plaintiffs named in Tuesday's suit — Don Davis, Stacey Johnson and Andrew Sasser — had previously been among the prisoners who challenged the lethal injection protocol Arkansas adopted in 2013 — which gave the ADC the authority to decide which drugs to use in performing lethal injections — as a violation of separation of powers. The suit made its way to the Arkansas Supreme Court, which ruled in a closely divided decision in 2015 that the execution method statute was lawful.

Arkansas Rep. Jeffrey Reed Wardlaw, a Republican, supported Act 302 in part as a response to a June 2024 mass shooting in Dallas County, Arkansas, that left four people dead and 11 injured. The person convicted for the shooting, Travis Eugene Posey, ultimately pled guilty to avoid the death penalty and was sentenced to life without the possibility of parole.

In the Tuesday complaint, the death row prisoners contested the law's provision giving the Division of Corrections "absolute, unregulated and undefined discretion" in determining the method it will use to carry out the death penalty.

Fraley noted that, while the state has laid out specific requirements for lethal injections dealing with drug sourcing, sterility and training of executioners, the statute includes none as applied to nitrogen asphyxiation.

"We don't know what's the quality or quantity of nitrogen that would be used. How would it be administered? Would it be a mask? Would it be a hood? Would it be a chamber?" Fraley said.

Robin M. Maher, the executive director of the Death Penalty Information Center, told Law360 on Wednesday that the law was "breathtaking" in its approach and raised questions about "why state officials are trying to keep the public in the dark."

"It gives blanket authority to an unelected official to change the method of execution that was selected by juries, and the legislation does not provide the public, or even the prisoners, with any details about the use of a method that has been shown to cause pain and suffering when used elsewhere," she said.

--Editing by Melissa Treolo.