[glennaro]

They could also use carbon dioxide instead of nitrogen, but then there's global warming or climate change or whatever the phrase du jour to consider. Wouldn't want the convicted murderer to endanger the Earth on his way out now, would ya?

[Lonesome in Massachussets]

Carbon dioxide poisoning is quite painful. Respiratory distress is caused by the inability to remove CO2 from the blood. Respiration is controlled by sensing CO2 levels. There was a village in Africa that was wiped out about 10 years ago when a volcano caused a local build up of CO2. An excruciating way to die. Carbon Monoxide is deadly, but much slower. It bonds to hemoglobin preventing the absorption of oxygen, but it is a very slow and nauseating process. If I had to be executed, I would probably choose nitrogen asphyxiation over any other method.