A man convicted of killing an elderly couple in 2004 is set to be executed by Alabama on Thursday, which will make him the second man executed in the state this year and the sixth in the country.

The execution of Jamie Ray Mills, 50, comes about four months after that of Kenneth Eugene Smith, who was put to death by nitrogen gas despite his objections to the method.

Alabama Attorney General Steve Marshall noted in a statement that Smith's execution "marked the first time in the nation – and the world – that nitrogen hypoxia was used as the method of execution," saying the state "has achieved something historic." Four days after that execution, Marshall filed a motion to set Mills' execution date, writing that “it was time for his death sentence to be carried out.” 

“There is no doubt that Mills committed those offenses," he wrote. "Mills' convictions and sentence are final."

The Alabama Supreme Court approved Marshall’s request for execution on March 20, allowing Alabama Gov. Kay Ivey to set Thursday's execution.

Here’s everything to know about Mills' execution.

Jamie Mills execution date, time set  

Mills is set to be executed at William C. Holman Correctional Facility in Atmore, about 50 miles northeast of Mobile.

The execution is not set for a specific time but rather a 30-hour window that will begin at 12 a.m. Thursday, May 30, and end at 6 a.m. on Friday, May 31, according to reporting by The Montgomery Advertiser, part of the USA TODAY Network. 

Mills will be put to death by lethal injection, considered a “primary method” of execution by all states and the federal government, according to the Death Penalty Information Center. 

The kinds of drugs or combination of drugs vary across jurisdictions, with states using one, two, or three drugs to put inmates to death. The drugs vary depending on availability and many states have struggled to obtain the drugs as sometimes overseas suppliers decline to be involved in the death penalty.

“Most three-drug protocols use an anesthetic or sedative, followed by a drug to paralyze the inmate, and finally a drug to stop the heart. The one- and two-drug protocols typically use an overdose of an anesthetic or sedative to cause death,” according to the Death Penalty Information Center.

The Alabama Department of Corrections has not answered USA TODAY's request for which drug or drugs they plan to use on Mills.

They also haven't said what his last meal request is.

More:Alabama governor sets 2nd execution using controversial nitrogen gas method

Mills seeks relief, attempts to delay execution with litigation

This week the 11th Circuit Court of Criminal Appeals denied two defense motions seeking a delay in Mills' execution The defense can still seek a stay from the U.S. Supreme Court.

Mills argues that ex-wife JoAnn Mills, who testified against him in connection with the 2007 murders of Floyd and Vera Hill, lied on the stand. Floyd, 87, and Vera, 72, were beaten to death and robbed in their home in Guin, about 70 miles northwest of Birmingham.

JoAnn Mills was considered a key witness in the case, testifying that she saw her husband kill the Hills with a ball peen hammer, tire tool and a machete, according to court documents filed in Marion County.  The couple was arrested a day after the murders, and were found with an assortment of items that connected them to the crime scene, court records show, including the suspected murder weapons in their car.

Jamie Mills asserted that the physical evidence collected not only proved his innocence, but supported the theory that he was framed by a local drug user he says had access to his vehicle on the night the Hills were killed.

He says it calls into question “not only the reliability of the capital trial verdict in this case, but also the integrity of the court,” according to the April 5 motion. About two weeks later, Jamie Mills filed another motion alleging that he might be strapped to the execution gurney for an extended period of time, which he says is “unnecessarily cruel."

There is an “imminent risk” at play, his attorneys argue in the April 26 filing, saying that he could be subject to an “ unnecessarily prolonged and tortuous execution at the hands of state officials” with unreviewable authority. 

Jamie Mills has asked the court for access to his attorney over the course of the execution, citing examples of four inmates were either executed or were subject to attempted executions that he argues were carried out improperly and caused unnecessary suffering. 

Alabama attorney general address Jamie Mills' claims

All of the allegations Jamie Mills has brought forth in the weeks leading up to his execution could have been made earlier, according to a May 17 response by Republican Attorney General Steve Marshall. 

“For a condemned inmate without the law or facts on his side, the best chance of delaying his execution is by filing multiple lawsuits in hopes of overwhelming the Eleventh Circuit and Supreme Court at the last minute,” causing the execution to be carried out under a "compressed or untenable timeline,” according to court records.

Jamie Mills has yet to provide any new evidence that could actually help clear his name, and instead he is “unwilling to believe that JoAnn might have simply done the right thing in testifying against him," according to Marshall.

JoAnn Mills was only offered a life sentence instead of the death penalty because of the "sincerity and remorsefulness" she showed on the stand, according to Marshall.

Claims by Jamie Mills about the validity of JoAnn Mills' testimony were “improper, untimely, and meritless,” serving as a way to a “further delay the execution,” Marshall wrote. 

He also dismissed concerns of unnecessary cruelty that Mills could face at the hands of the corrections department, saying there's no data to support the claim that he could be strapped to a gurney for an “unconstitutionally long time.” Marshall says that there is no constitutional right that would grant Jamie Mills the ability to have lawyers in the execution chamber.

Courts reject last-minute appeals from Jamie Mills

Two federal judges denied Mills’ petitions for relief last week, both stating that he could have brought the information forward “several years ago.” 

Emily Marks, a judge for the Middle District Court of Alabama, wrote in a May 21 response that the claims made against the the corrections department were “barred by statute of limitations.” 

The delay in making these claims known recently is “unreasonable, unnecessary, and inexcusable … The practice of filing lawsuits and requests for stay of execution at the last minute where the facts were known well in advance is ineffective, unworkable, and must stop,” Marks wrote. 

Marks did acknowledge that the correction department has been known on “several occasions” to subject inmates − including Joe James, Alan Miller, and Kenneth Smith − to “prolonged executions or execution attempts during which those inmates were unnecessarily strapped to the execution gurney.” 

But it was up to Mills to bring the allegations forward sooner, Marks wrote.

Contributing: Amanda Lee Myers and Marty Roney