Alabama performs 1st nitrogen gas execution: What to know about this method

Kenneth Smith, from Alabama, on Thursday, was the first person executed with nitrogen gas. Experts said concerns have been raised about whether or not it is cruel.

An Alabama man has become the first ever person executed via a new method, nitrogen gas, on Thursday.

Kenneth Eugene Smith, 58, was sentenced to death for his alleged role in the 1988 murder of Elizabeth Sennett. Her husband, Charles Sennett, allegedly hired someone -- who, in turn, hired two men, including Smith -- to kill his wife and make it look like a burglary gone wrong.

Smith was to be executed in November 2022 via lethal injection, but, despite multiple attempts, officials were not able to insert an intravenous line to administer the drugs before the death warrant expired.

However, medical and legal experts told ABC News that nitrogen gas as a method for execution is untested and there's no evidence the method will be any more humane or painless than lethal injection.