Lawyers for a group of South Carolina death row inmates who have run out of appeals argued to the state's Supreme Court that two of the state's forms of execution — the old electric chair method and the new firing squad method — are cruel and unusual punishments, although the state claims that "painless" deaths are not mandated.

The lawyers for the four inmates also argued that a 2023 law created to allow lethal injections to restart hides too many details about the new drug and protocol used to kill inmates.

This, as 33 inmates sit on South Carolina's death row. There has not been a formal moratorium on the death penalty, but the state has not performed an execution in nearly 13 years after the drugs it used for lethal injection expired and companies refused to sell more to prison officials unless they could hide their identities from the public.

South Carolina purports that all three execution methods are consistent with existing protocols, saying "instantaneous or painless" executions are not mandated by law.

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"Courts have never held the death has to be instantaneous or painless," wrote Grayson Lambert, a lawyer for Republican Gov. Henry McMaster's office.

During a hearing, the justices questioned whether the firing squad should be considered a banned unusual punishment since it has only been used in the U.S. three times in the past 50 years, all of which were carried out in Utah. They also questioned the electric conductivity of the human skull and asked if modern science has found the electric chair to be more painful and cruel than a century ago.

A lawyer for the inmates admitted that if the court bans electrocution and the firing squad, and if the state can show the drugs used for lethal injection are the right potency and purity and the method matches what is used by other states and the federal government, then they do not have a basis to stop an execution.

"I want to make sure it is humane as possible," attorney John Blume said.

If the justices allow executions to restart and any additional appeals are unsuccessful, South Carolina's death chamber could start receiving inmates again after going unused since May 2011.

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While four inmates are suing, four others have also run out of appeals, but two of them face a competency hearing before they can be executed, according to the South Carolina non-profit Justice 360, which says it fights for fairness and transparency in death penalty and other major criminal cases.

South Carolina asked the Supreme Court to throw out a lower court ruling after a trial in 2022 found that the electric chair and the firing squad are cruel and unusual punishments.

Circuit Judge Jocelyn Newman sided with the inmates, whose experts testified prisoners would feel terrible pain whether their bodies were "cooking" by 2,000 volts of electricity in the chair or if their hearts were stopped by bullets from the firing squad, assuming the three shooters hit their target.

The state's current execution law requires inmates to be sent to the electric chair unless they select an alternative method.

Lawmakers allowed a firing squad to be added to the possible methods in 2021. No legislation has been proposed in South Carolina to add the controversial nitrogen gas method, which was used in the U.S. for the first time to kill inmate Kenneth Eugene Smith in Alabama last month. In this method, Smith breathed in pure nitrogen gas through a face mask.

Attorneys for the inmates argue South Carolina's shield law is more secretive than any other state and that prison officials should not be allowed to hide the identities of drug companies, the names of anyone helping with an execution and the exact procedure followed.

In September, prison officials announced they now have the sedative pentobarbital and changed the method of lethal injection execution from using three drugs to using only one. Few other details were released outside of saying South Carolina's method is similar to the protocol followed by the federal government and six other states.

Lawyers for the prisoners said most states release at least some information about the potency, purity and stabilization of lethal injection drugs.

The prisoners' lawyers argue pentobarbital, compounded and mixed, has a shelf life of about 45 days. They are asking for information about whether there is a regular supplier for the drug and what guidelines are in place to test the drug and make sure it is what the seller claims.

If the drug is not potent enough, inmates may suffer without dying, according to court papers. If it is too strong, the drug molecules can form tiny clumps that would cause intense pain when injected.

"No inmate in the country has ever been put to death with such little transparency about how he or she would be executed," Justice 360 lawyer Lindsey Vann wrote.

Lawyers for the state claim the inmates want the information so they can determine who is supplying the drugs and put them under public pressure to stop.

"Each additional piece of information is a puzzle piece, and with enough of them, respondents (or anyone else) may put them together to identify an individual or entity protected by the Shield Statute," Lambert wrote.

The justices appeared to believe the shield law was too narrow, with several suggesting requiring the prisons director to at least release a statement explaining why he believes the drugs are alright to use, whether it is through independent testing or in-house action at the prison.

South Carolina used to carry out an average of three executions a year and had more than 60 inmates on death row when the last execution was carried out in 2011. However, successful appeals and deaths have lowered the number of people currently on death row to 33.

Prosecutors have sent only three new prisoners to death row in the past 13 years. Amid rising costs, the lack of lethal injection drugs and more vigorous defenses, prosecutors are instead accepting guilty pleas and life in prison without parole.

The Associated Press contributed to this report.