59-year-old Alan Eugene Miller was declared dead at 18:38 local time on Thursday at the prison in southern Alabama. He had then shaken and trembled for about two minutes, followed by about six minutes of gasping for breath, reports AP.
In an execution by nitrogen gas, the condemned person dies from asphyxiation when 100 percent nitrogen is introduced into the body through a breathing mask, which leads to oxygen deprivation.
Alan Eugene Miller was sentenced to death for workplace shootings in 1999 where three people he worked with were killed, writes The Guardian.
Five condemned men in five states in the USA have been executed in the last six days, which is an unusually high number.
The first execution by nitrogen gas was also carried out in Alabama, in January this year. The execution was sharply criticized by, among others, the UN's human rights chief Volker Türk, who described the method as torture.
