A Death Row inmate in Alabama is set to be the first prisoner to ever be executed by a new method.
When most people think of prisoners on death row, the electric chair comes to mind as something that would send shivers up a criminal's spine.
Most executions in the modern day are done through lethal injection, which is generally judged to be more humane.
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But a new execution method has remained untested on humans - until now.
So, what is this new execution method?
It's called Nitrogen hypoxia, and who on death row is set to be subjected to this new method? None other than Kenneth Smith.
Smith was convicted of capital murder and sentenced to death in 1989, and then again in 1996.
Smith had been hired by Charles Sennett, the pastor of Westside Church of Christ in Sheffield, Alabama to murder his wife.
The murder was carried out in exchange for a large insurance policy and a payment of $1,000.
Alongside his friend John Parker, he ambushed Sennett's wife, Elizabeth and subjected her to horrific attacks. She was punched, beaten, bludgeoned and stabbed over ten times with a six inch survival knife.
Smith has spent the last three decades in prison after surviving three previous attempts to execute him via lethal injection.
The last attempt to put Smith to death happened in November 2022, which, according to his legal team, saw him be strapped to an execution gurney for up to four hours as prison officials struggled to find a vein where they could administer the lethal injection.
Last year, it was decided by Alabama Attorney General Steve Marshall that Smith would be killed by a new execution method.
Although its use in executions has already been authorised by three states - Alabama, Oklahoma and Mississippi - it has never been used before.
How does it work?
The prisoner is forced to breathe in nitrogen through a respirator placed over the mouth and nose. As a result of oxygen deprivation, they die.
According to the attorney general's office, the method is highly effective and causes the subject to fall unconscious within seconds.
Death quickly follows in a matter of minutes.
Smith's lawyer has lodged appeals against the decision to execute his client via nitrogen hypoxia, claiming he is a 'test subject'.
The method has also been ruled as unsuitable for use on small mammals other than pigs by veterinary scientists in the US and Europe.
Speaking to The Guardian, David Morton, professor of biomedical science at the University of Birmingham, said: "It is effective, but it can cause severe distress before unconsciousness and death ensue. In effect it is a suffocation method.
"It is likely also that there will be considerable species variation, and we are not sure what will happen in humans.
"Animal experiments are usually used as a proxy for humans, but not so in this case it seems – the ultimate test is being carried out using a human being."
Smith is set to be killed on 25 January.
Ben Thompson