The attorney general tweeting his acceptance, the execution of Ronnie Lee Gardner (he had the three name thing down) commenced. He earlier talked with a bishop of the Church of Latter Day Saints, suggesting perhaps his desire for a firing squad reflecting "blood atonement" beliefs shared by some members of that faith. It is a major reason why states like Utah and Idaho (until recently) retained that method of execution.
Family of the victim had earlier joined an attempt to obtain a reprieve, suggesting the victim opposed the death penalty, and would not want his death answered with an execution. A person shot in the escape attempt that led to the murder did not share similar feelings; Gardner was in court at the time on a charge of murder during a robbery.
A "troubled life marred by drugs, sexual abuse and indiscriminate violence" suggests that the deterrence effect of the execution is questionable, given such a life leads to reckless acts no matter what the possible consequences. Various potential problems with the case led it to linger for over twenty years, the apparent reason why Justices Stevens and Breyer supported (citing earlier quest to hear case where person lingered on death row for decades) taking his case down to the very end.
At this point, Gardner's death appears to amount mainly as retribution, defended by the Supreme Court a few decades this way:
The instinct for retribution is part of the nature of man, and channeling that instinct in the administration of criminal justice serves an important purpose in promoting the stability of a society governed by law. When people begin to believe that organized society is unwilling or unable to impose upon criminal offenders the punishment they "deserve," then there are sown the seeds of anarchy -- of self-help, vigilante justice, and lynch law. ...
[T]he decision that capital punishment may be the appropriate sanction in extreme cases is an expression of the community's belief that certain crimes are themselves so grievous an affront to humanity that the only adequate response may be the penalty of death.
Justice Marshall disagreed, arguing that total destruction of the human person by the state robs diminishes the value that the Cruel and Unusual Punishment Clause protects while also constitutionally excessive since alternative punishments are available. In part:
Retribution surely underlies the imposition of some punishment on one who commits a criminal act. But the fact that some punishment may be imposed does not mean that any punishment is permissible.
We require someone to commit a wrong to punish (mere safety doesn't warrant prison; you need to commit a crime ... safety might warrant a mental institution) . In some way, this is more mere deterrence, a type of "retribution." See also, "punitive" damages that punish, not just compensate. But, even if we accept that, and look past the dangers of our imperfect system of justice [which I cannot -- life only taken by due process of law], taking a life is a step beyond. We don't rape rapists, maim those who maim, and we shouldn't kill those that kill.
To the degree vengeance or more carefully applied "retribution" requires it given the realities of society today, it is a force of power, not rightful law.*
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* Justice Chase, signer of the Declaration of Independence, put forth the basic principle over two hundred years ago, a few years before Marbury v. Madison expressed the principle of judicial review: "An act of the Legislature (for I cannot call it a law) contrary to the great first principles of the social compact, cannot be considered a rightful exercise of legislative authority."
As to the technique itself, in respect to pain and safety, it seems marginally different from lethal injection. That isn't the only way to judge modern standards of decency, however, and the spectacle of it all might be deemed barbaric as well. But, as suggested before, lethal injection isn't that grand in that department either. Still, arbitrary culturally accepted standards just might past muster, especially under Baze v. Rees ("dignity of procedure" is a legitimate purpose for perhaps risky paralyzing agent).