Lawyers for Louisiana and death row inmate Jessie Hoffman Jr. have agreed to unseal the state's nitrogen gas execution protocol, which was being kept secret from the public until now.

A death row inmate slated to become the first person to be put to death by nitrogen gas in Louisiana is seeking to halt the execution, citing constitutional concerns over the controversial killing method.

Christopher Sepulvado, 81, died Saturday at the Louisiana State Penitentiary in Angola, Louisiana, "from natural causes as a result of complications arising from his pre-existing medical conditions," according to the Louisiana Department of Public Safety and Corrections.

Louisiana's nitrogen gas execution protocol hasn't been released to the public. "It relates to the most solemn … government action that the government can take, which is to take somebody’s life," said the lawyer for Jessie Hoffman,

Hours after the nation’s first execution by nitrogen gas in January last year, Alabama's attorney general urged other states to also develop it as a method for carrying out death sentences. Now, some states are following suit.

A death row inmate in Louisiana who is scheduled to become the first person in the state to be executed using nitrogen gas has asked for his capital punishment to be carried out using a more “humane” method.