Second inmate braces for nitrogen hypoxia execution as Alabama looks to continue 'brutal' killings after first was left 'thrashing' for five minutes in 'house of horrors' death chamber

Alabama is preparing to execute a second inmate via nitrogen gas hypoxia despite the first attempt being described as 'torture' and the 'most violent' execution in modern US history. 

On Thursday, Alan Eugene Miller, 59, is set to be put to death for the 1999 murders of three of his co-workers when he gunned them down over rumors about his sexuality.

Unless there is a last-minute stay of execution, the killer will be strapped to the same gurney as Kenneth Eugene Smith, who endured the first nitrogen execution in January. 

Smith was said to have thrashed and retched against his restraints for a 'horrific' 22-minute ordeal, as a firefighters-style mask placed over his face filled with 100 percent nitrogen gas that suffocated him to death. 

Officials in Alabama turned to nitrogen gas as an execution method due to widespread issues with obtaining lethal injection drugs in recent years. 

While some states have taken to extending the expiration dates of their drugs against warnings from human rights organizations, others have also looked at bringing back firing squads and electric chairs. 

Alabama officials insist that nitrogen hypoxia is a painless and humane execution method, and maintained that stance despite backlash over Smith's reportedly agonizing death. 

One of the journalists in the viewing room when Smith was executed, Lee Hedgepath, said the hitman was 'He's shaking so violently that the bottom of the gurney where the metal frame meets the ground came off the floor.' 

Smith reportedly shook and strained against his restraints on the gurney for several minutes, and only weakened as he suffocated. 

He then began retching in his mask and remained conscious for minutes more, and after his eventual death witnesses emerged from the room shaken and confused. 

The killer's spiritual guide Rev. Jeff Hood, who held a bible to Smith as he died, said the execution was by far the 'worst' of the dozen-plus executions he had witnessed.  

Miller faces the same fate on Thursday, over 25 years since he opened fire on his co-workers at a welding supply store in Pelham, Alabama. 

The 1999 slayings of his victims, Terry Jarvis, Lee Holdbrooks and Christopher Yancy, unfolded because Miller believed Jarvis told the other men that he was gay. 

He burst through the doors of his former workplace with a firearm, and exclaimed: 'I'm tired of people starting rumors on me.' 

He shot Yancy, 32, and Holdbrooks, 28, multiple times before fleeing in his truck and driving nearby to shoot Jarvis. 

When he found Jarvis, he shouted to him: 'Hey, I hear you've been spreading rumors about me.' 

Although Jarvis denied he was spreading rumors, Miller shot him several times, and he died later in hospital. 

Miller was arrested hours later in his truck, where he was discovered alongside a Glock firearm and a spent ammunition magazine. 

A jury convicted him of the murders and sentenced Miller to death, despite a psychiatrist testifying that he was 'mentally ill' during the shooting spree. 

According to his federal appeals, Miller's family has an extensive history of mental illness tracing back at least four generations, reports USA Today. 

Facing the prospect of nitrogen execution, Miller has filed a lawsuit challenging the method on the basis of Smith's violent death earlier this year. 

Alabama Attorney General countered that Smith's execution was 'textbook', and said last month: 'Miller's execution will go forward as planned.'