There are just a matter of days left for the most controversial execution method in recent times, which take place as Death Row inmate Kenneth Eugene Smith awaits death's door.
The Alabama prisoner and hitman was sentenced to Death Row for his crimes in 1988 after he was hired by Charles Sennett, the pastor of the Westside Church of Christ in Sheffield, Alabama, who wanted his wife Elizabeth murdered in exchange for an insurance policy.
Smith and his accomplice, John Parker, were paid $1,000 each for the murder, which saw Elizabeth punched, beaten, bludgeoned, and stabbed over and over again with a six-inch survival knife.
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Elizabeth suffered a total of ten stab wounds - eight to her chest and two to her neck - which proved fatal.
The hitman was eventually convicted of capital murder.
Smith who has previously survived execution by lethal injection, is now set to be judicially killed on 25 January by new controversial execution method, nitrogen hypoxia.
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The untested method involves breathing in nitrogen through a respirator mask placed over the inmate's nose and mouth - killing them as a result of oxygen deprivation.
Doctor Jeffrey Keller has stressed that the process is 'entirely experimental' and 'nobody knows' what's going to happen.
"There is some concern that leaking nitrogen could affect bystanders, and I don’t know if that’s true, because nobody knows," he told The Marshall Project.
"It’s also proposed to be painless, and I know that is wrong: The proponents refer to people who have become nitrogen-intoxicated during airplane flights, or scuba diving, and then woke up and reported they didn’t feel anything.
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"But the incarcerated person knows exactly what’s going to happen."
The doctor continued: "This is no different from lethal injection, in that sense.
"Just as if you don’t hold your arm still, it’s harder to start an IV line, if you don’t hold your head still, it’s harder to get a seal.
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"Regardless of the cooperation, we’re not using medical experts, having an anesthesiologist fit the mask or titrate the nitrogen, someone who has done this hundreds and hundreds of times."
When answering a question about chance of vomiting or seizures, Dr Keller explained: "The assumption is often that this is going to go perfectly. But as with lethal injection, as more of these are done, everything that can go wrong will eventually."
With regards to potential issues with the respirator mask, he added: "EMTs in ambulances will find someone with hollow cheeks, or who has taken their false teeth out, will have trouble forming a seal with a mask.
"Or talk to firefighters. If they’re going to run into a burning building, they have to have their masks perfectly fitted, and it’s not one-size-fits-all. A firefighter who gains or loses 50 pounds needs to get a new mask.
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"They are not allowed to have facial hair because it interferes with the seal."
When Smith's execution was given the green light last week, it received backlash from various parties.
This included the UN high commissioner for human rights in Geneva, who classed the method as inhumane, while veterinary scientists in the US and Europe compared it with being unacceptable for most small mammals.