Kenneth Smith, who was convicted in the 1998 murder-for-hire killing of Elizabeth Sennett, became the first person ever in the United States to be executed by nitrogen gas. State officials have testified in court that this method is "painless and humane," but it remains controversial. NBC’s Emilie Ikeda reports for TODAY. » Subscribe to TODAY: youtube.com/@TODAY About: TODAY brings you the latest headlines and expert tips on money, health and parenting. We wake up every morning to give you and your family all you need to start your day. If it matters to you, it matters to us. We are in the people business. Subscribe to our channel for exclusive TODAY archival footage & our original web series. Connect with TODAY Online! Visit TODAY's Website: today.com Find TODAY on Facebook: facebook.com/today Follow TODAY on Twitter: twitter.com/TODAYshow Follow TODAY on Instagram: instagram.com/todayshow » Stream TODAY All Day: ww...