The Oklahoma botched execution has prompted 21 death row inmates from the state to file a lawsuit against prison officials to prevent them from using "untested and unsound" execution methods.

The complainants wrote in the lawsuit alleging that the procedures used by the state "create a substantial risk of severe pain, needless suffering and a lingering death." 

According to these death row inmates, Oklahoma's lethal injection practices violate the constitutional rights of the prisoners. They also argued that the state officials did not consult experts in the development of procedures and that the drugs being used are not suitable for executions.

"In the aftermath of Clayton Lockett's horrifically bungled execution at the end of April, there are so many unanswered questions about whether Oklahoma can humanely carry out executions," Megan McCracken of the UC Berkeley School of Law's Death Penalty Clinic told The Los Angeles Times, Wednesday.

The complainants particularly condemn the use of midazolam, an anesthetic "incapable of producing a state of unawareness that will be maintained after either of the other two pain-producing drugs, vecuronium bromide (or its substitute) and potassium chloride, is injected," reports the Agence France-Presse. Even the U.S. Food and Drug Administration has till now not approved the midazolam, used as a stand-alone anesthetic.

The move comes two months after Oklahoma death row inmate, Clayton Lockett, was given a combination of three untested lethal drugs. He writhed in pain and died of a massive heart attack 45 minutes after the drugs were administered.

Another death row inmate in the state, Charles Warner, was scheduled to be executed two hours after Lockett. However, authorities ordered a six-month stay on his execution. The new date for his execution is set for Nov. 13. Warner now heads the list of plaintiffs in the lawsuit. Warner was convicted of raping and killing an 11-month-old, Adrianna Waller.

According to a spokeswoman for Oklahoma Attorney General Scott Pruitt, the officials were reviewing the filing.  The Department of Corrections does not comment on pending litigation, spokesman Jerry Massie said.

 "By attempting to conduct executions with an ever-changing array of untried drugs of unknown provenance, using untested procedures, the defendants are engaging in a program of biological experimentation on captive and unwilling human subjects," the lawsuit states, according to the Associated Press.