Alabama death row inmate first to be executed by nitrogen gas

Kenneth Eugene Smith, on death row in Alabama, is set to be the first US inmate to be executed using nitrogen gas after losing his last minute appeals.

His lawyers described the punishment as "cruel and unusual", something that the UN agree with after they objected to the plans a few weeks ago.

Smith has been on death row for 35 years after being convicted of murdering Elizabeth Sennett in 1989. She was beaten with a fireplace implement and stabbed in the chest and neck, and her death was staged to look like a home invasion and burglary.

Smith was one of two people convicted for the murder and were paid $1,000 by her husband, a preacher who had become heavily in debt. It was thought he wanted his wife dead so he could claim the insurance money.

Smith's fellow hitman, John Forrest Parker, was executed in 2010, and Sennett's husband killed himself as investigators closed in on his arrest.

The UN's High Commissioner for Human Rights has said gassing Smith could amount to torture or other cruel, inhuman or degrading treatment, and called for a halt.

Breathing pure nitrogen without oxygen causes the cells to break down and leads to death. Alabama said in a court filing that they expect him to lose consciousness within seconds and die in a matter of minutes.

But its use has been denounced by some medical professionals, who warn it could cause a range of catastrophic mishaps, ranging from violent convulsions to survival in a vegetative state.

Alabama and two other US states have approved the use of nitrogen hypoxia as an alternative method of execution because the drugs used in lethal injections have become more difficult to find.

Alabama already tried to execute Smith by lethal injection two years ago but were unable to raise a vein before the state's death warrant expired.

The state has 30 hours to carry out the execution, which involves pumping nitrogen gas through a mask, from Thursday at 6am GMT.