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Crime scene police line | Representational Image Photo: GETTY IMAGES / SCOTT OLSON

The US state of Alabama has executed a convicted murderer using the method of nitrogen asphyxiation. This is the first time that the method of capital punishment has been used in the country.

Kenneth Eugene Smith was convicted in 1989 for murdering a pastor's wife in a killing-for-hire. Smith had appealed to the US Supreme Court for a stay on the execution, stating that the method was cruel.

In 2022, the prison officials tried and failed to carry out the execution by administering a lethal injection to Smith. According to local media reports, the officials could not set intravenous lines to administer the injection.

He was one of two men convicted of murdering Elizabeth Sennett in March 1988. The woman was beaten with a fireplace implement and stabbed in the chest and neck. The crime scene was made to look like a burglary, per a BBC report.

The entire plan was orchestrated by her debt-ridden husband Charles Sennett so he can collect the insurance money after his wife's death. He killed himself a week after her death, while Parker was executed by lethal injection in 2010.

Smith is the first person in the world to be put to death using pure nitrogen gas, according to the Death Penalty Information Center.

He was pronounced dead on Friday by the state attorney general. "Justice has been served. Tonight, Kenneth Smith was put to death for the heinous act he committed over 35 years ago," the statement by Attorney General Steve Marshall said.

He "began writhing and thrashing for approximately two to four minutes, followed by around five minutes of heavy breathing," local media Al.com quoted the witnesses as saying.

Last week, the UN's High Commissioner for Human Rights had appealed to halt the execution stating that it amounted to torture under international human rights law.

The execution was carried out at Holman Prison in Atmore, Alabama, by nitrogen hypoxia, which involves pumping nitrogen gas into a facemask, causing death due to a lack of oxygen, known as hypoxia. Nitrogen hypoxia is currently not used as an execution method anywhere in the world.

The last such execution was carried out in 1999, when a convicted murderer was put to death using hydrogen cyanide gas.

The United States carried out 24 executions last year, and all of them involved administering. As many as 23 US state have abolished capital punishment, while the governors of states like Arizona, California, Ohio, Oregon, Pennsylvania and Tennessee have put a hold on its use.

Alabam, Oklahoma, and Mississippi are the three US states that have approved the use of nitrogen hypoxia as a method of execution.

In 2015, the state of Oklahoma put to death child-killer Charles Warner using a controversial drug last used in the botched execution of Clayton Lockett in April 2014.

Warner, who had raped and murdered 11-month-old girl Adrianna Waller, was executed on January 15 January, 2015, using the same combination of drugs but with five times the dosage of midazolam used to sedate Lockett.

When Warner was asked if he had any final words as he was strapped down and had intravenous drips inserted, he said: "Before I give my final statement, I'll tell you they poked me five times. It hurt. It feels like acid".

He later added: "My body is on fire. No one should go through this. I'm not afraid to die. We's all going to die".

Lockett, the Oklahoma prisoner who died in agony in a botched execution, was tasered hours before and had cut his own arm.

Lockett, a convicted murderer, died of a heart attack 43 minutes after being injected with an experimental cocktail of drugs in 2014. The United Nations had said that the execution of the 38-year-old may constitute cruel, inhuman, and degrading treatment under international law.