A man sentenced to death was executed with nitrogen in the United States on Thursday evening, making him the second person ever to be executed using the method. Alan Miller, who had been convicted of murdering three people at his workplace over 20 years ago, died in Shelby County, Alabama, the US Death Penalty Information Center reported. During the procedure, he was supplied with nitrogen through a face mask, which resulted in death from a lack of oxygen. The first execution in the US using this method took place in Alabama in January. In that case, eyewitnesses reported that the person strug…