Louisiana plans to use nitrogen gas to execute death row inmate Jessie Hoffman next week. Here's what to know about the method and why its controversial.

The US Supreme Court, in a 5-4 ruling just hours before the execution, declined to halt the execution. On Friday, a federal appeals court vacated a preliminary injunction blocking the execution granted by a lower judge.

In a failed last-ditch appeal to the U.S. Supreme Court, lawyers for condemned inmate Jessie Hoffman had argued that executing someone with nitrogen gas produces unconstitutional "psychological terror.