In the U.S., the death penalty has been abolished in 23 states, while six others are under a moratorium on executions, reflecting a broader decline in support for capital punishment.

Miller's execution follows a previous attempt in September 2022 that was aborted due to difficulties in establishing intravenous access for lethal injection.

Convicted in 2000 for a 1999 workplace shooting spree that resulted in the deaths of three men, Miller's case has drawn significant attention.

Alan Eugene Miller, a 59-year-old man from Alabama, was executed using nitrogen gas, marking the second instance of this method being used in the U.S.

Despite initially challenging the nitrogen gas method, Miller settled with the state last month, agreeing to proceed with the execution under Alabama's alternative to lethal injection.

Alabama became the first state to execute a prisoner using nitrogen hypoxia in January 2023, raising concerns about the method's humanity and effectiveness.

Alabama Attorney General Steve Marshall has defended nitrogen hypoxia as 'swift, painless and humane,' despite eyewitness accounts of distress during the first execution.

Death penalty opponents are urging Governor Kay Ivey to halt Miller's execution, citing issues that arose during the execution of Kenneth Smith.

Witnesses reported that Miller exhibited physical distress during the execution process, including shaking and gasping.

In his final words, Miller claimed, 'I didn't do anything to be in here,' highlighting the ongoing controversy surrounding his conviction.

The discussion around execution methods continues to evolve, with increasing scrutiny on the implications of nitrogen hypoxia and its potential for causing suffering.

Human rights advocates have criticized nitrogen hypoxia as a form of 'human experimentation,' arguing that no execution method can truly be deemed humane.