(AP) — Alabama is preparing to carry out the nation’s second nitrogen gas execution this week, as sharp disagreements continue over the humaneness of the new method. Alan Eugene Miller, 59, is scheduled to be executed with nitrogen gas at the William C. Holman Correctional Facility in Atmore, the Montgomery Advertiser reported. The window for the execution opens at midnight ET on Thursday and expires Friday at 6:00 a.m. ET, according to ABC News. Alex Jones’ Infowars will be liquidated at auction to help pay Sandy Hook families Miller was convicted of killing three men in back-to-back workplace shootings in 1999. Officials escort murder Alan Eugene Miller away from the Pelham City Jail in Alabama on Aug. 5, 1999. (AP Photo/Dave Martin, File) The execution is moving forward after the state and Miller reached an undisclosed settlement agreement to end his lawsuit challenging the new method. The new execution method uses a respirator gas mask, which is placed over the inmate’s face, to replace breathable air with pure nitrogen gas, causing death by lack of oxygen. Alabama carried out the first nitrogen gas execution in January with the execution of Kenneth Smith. Smith shook and writhed on the gurney for at least two minutes, followed by several minutes of slow gasping breathing. The execution lasted approximately 22 minutes, which included the time for Smith to make his final statement. ‘Extreme Makeover: Home Edition’ star dies after reported stabbing Alabama Attorney General Steve Marshall in January said that, “Alabama’s nitrogen hypoxia system is reliable and humane.” He called Smith’s execution “textbook.” In court filings, the state has disputed that Smith’s shaking movements were proof But death penalty opponents and advocates for other inmates facing nitrogen execution maintain that what happened at Smith’s execution show that there are problems, or at least questions about, the new execution method. Nexstar's Ashleigh Jackson contributed to this story.