Alan Miller shook and trembled on gurney after becoming second person to be executed by controversial technique

Alabama has carried out the second execution in the US using the controversial method of nitrogen gas, an experimental technique for humans that veterinarians have deemed unacceptable in the US and Europe for the euthanasia of most animals.

Alan Eugene Miller, 59, was pronounced dead on Thursday evening at a south Alabama prison. The lethal method involves being strapped to a gurney, where a respirator mask is applied to the face and pure nitrogen piped in. The resulting oxygen deprivation will cause death by asphyxia.

Miller shook and trembled on the gurney for about two minutes with his body at times pulling against the restraints, followed by about six minutes of gasping breathing, according to the Associated Press.

Miller’s death is the latest in an extraordinary week in the US in which five condemned men in five states are set to be killed over six days. Three prisoners have already been executed – on Friday South Carolina killed Khalil Divine Black Sun Allah in its first execution in 13 years, then on Tuesday Texas killed Travis Mullis and Missouri put to death Marcellus Williams.