(CNN)A difficult execution in Alabama this week is raising well-tread questions about the humanity and appropriateness of lethal injections.
8 controversial executions that sparked lethal injection debates
Ronald B. Smith was put to death on Thursday night, and witnesses say he coughed and heaved during the process.
Smith's execution had been delayed twice, and his legal team had tried to delay it a third time, saying that Alabama's drug protocol would cause him to suffer, violating the Constitution's ban on cruel and unusual punishment.
Lethal injection has long inspired debate: How reliable is it in delivering quick, painless death? What drugs are necessary to ensure such an end?
There are several botched executions that serve as benchmarks in America's long and uncomfortable history with lethal injections. Here are some of them.
Joseph R. Wood, executed July 23, 2014, in Arizona: Wood's execution took two hours, and witnesses said he appeared to be in pain and gasping for breath. While interpretations of his last moments varied -- state officials and some of Wood's family said he was simply "sedated" -- Arizona Gov. Jan Brewer said the ordeal took too long and she ordered the state's Department of Corrections to review the case.
Dennis McGuire, executed January 16, 2014, in Ohio. Columbus Dispatch reporter Alan Johnson said the execution process took 24 minutes, and that McGuire appeared to be gasping for air for 10 to 13 minutes. He had been injected with midazolam and hydromorphone, a two-drug combination that hadn't been used before in the United States.
Clayton Lockett, executed April 29, 2014, in Oklahoma. Lockett was injected with midazolam, but instead of becoming unconscious, he twitched, convulsed and spoke. The execution was halted, but Lockett died after 43 minutes. A team that prepared Lockett for execution failed to set a properly functioning IV in his leg, according to preliminary findings of an independent autopsy.
Romell Broom, survived execution September 15, 2009, in Ohio: Broom's execution was halted by Ohio Governor Ted Strickland after a medical team tried for hours to puncture Broom's veins and administer the injections. Broom remains on death row in Ohio. In 2016, a second attempt at execution was approved by state courts, but Broom filed a petition to halt it.
Angel Diaz, executed December 12, 2006, in Florida: According to Diaz's attorney, the convicted killer's execution took 34 minutes, and he was in pain and trying to communicate through part of it. An autopsy revealed the needles put in Diaz's arm went through the veins, injecting the drug cocktail into the surrounding tissue. The incident prompted Florida Gov. Jeb Bush to suspend all executions in the state and appoint a commission to examine the "humanity, constitutional imperative and common sense" of lethal injection measures.
Jose High, executed November 7, 2001, in Georgia. This execution illustrates a common problem. The execution team had trouble finding a usable vein and spent 39 minutes looking before finally sticking a needle into High's hand. A second needle was inserted between his neck and shoulder by a physician. Sixty-nine minutes after the execution began, he was pronounced dead.
Joseph Cannon, executed April 23, 1998, in Texas. The needle popped out and Cannon said to witnesses, "It's come undone." The needle was reinserted and 15 minutes later a weeping Cannon made his second final statement.
John Wayne Gacy, executed May 10, 1994, in Illinois. Lethal chemicals solidified and clogged in the IV tube leading to Gacy's arm. A new tube was installed and the execution proceeded.