Justice Sonia Sotomayor speaking last fall. (Renee Jones Schneider/Star Tribune via Associated Press)

The Supreme Court said Tuesday that it would not hear the case of an Alabama inmate whose execution the justices delayed in November. This decision was accompanied by a critical dissent written by Justice Sonia Sotomayor, who questioned whether lethal injection — the primary method of execution in the United States — “appears humane [but] may turn out to be our most cruel experiment yet.”

Sotomayor’s explanation for this sentiment doubles as a modern history of the death penalty, which has been on the decline nationwide for years. In her 18-page dissent, she excoriates the use of midazolam, a sedative that Alabama uses in its lethal injection protocol and has cropped up recently in other executions that were apparently bungled or took longer than usual.

Early in her dissent, Sotomayor describes lethal injections in the United States as being “generally accomplished through serial administration of three drugs.” This is actually no longer the case, although it was when the Supreme Court, in 2008, upheld Kentucky’s lethal injection protocol and essentially ended a nationwide moratorium on executions.

How lethal injections have changed in the past decade

Since then, lethal injection drugs have become more difficult to obtain amid a shortage, and executions have become a fractured process, with different states using different chemicals and combinations. This fact, though, feeds into Sotomayor’s argument about the use of midazolam in executions that have drawn scrutiny, because it was this shortage and the ensuing scramble that led states to adopt midazolam.

The three-drug protocol Sotomayor outlines — an anesthetic, a paralytic and a drug that stops the heart — was used in most lethal injections until 2010, when the drug shortage, prompted in part by European objections to capital punishment, began to dry up the supply. State officials began scrambling to obtain other drugs and rewrite their lethal injection protocols in an effort to continue carrying out executions, but the drug shortages and legal challenges helped contribute to plummeting execution rates.

Executions and death sentences plummeted this year as capital punishment declined nationwide

One of the drugs added to the mix since the shortage began is midazolam, which a handful of states incorporated into their plans. Sotomayor, joined by Justice Stephen G. Breyer in her dissent on Tuesday, outlined what she calls the “terrifying” recent history of midazolam — with the most recent headline-generating incident occurring in December, when Alabama executed Ronald Bert Smith Jr.

A month before Smith’s execution, the Supreme Court stayed the execution of Thomas D. Arthur, a murderer on Alabama’s death row. Chief Justice John G. Roberts Jr. joined four other justices in voting to stay the execution, writing that he was doing this as a “courtesy vote” even though he did not believe the case merited a review. (Arthur’s case was the one the justices declined to hear on Tuesday.)

The same did not occur weeks later when Smith, sentenced to death for killing a convenience-store clerk during a robbery, sent his challenge to the justices. He was executed when a deadlocked Supreme Court did not step in.

After divided Supreme Court allows Alabama execution, inmate heaves and coughs during lethal injection

During the lethal injection, Smith apparently struggled for breath, heaved and coughed for about 13 minutes, according to media witnesses. Smith’s execution followed on the heels of three unusually long executions in 2014 that also involved midazolam. An Ohio inmate took nearly 30 minutes to die, while an Arizona inmate’s execution took nearly two hours while he gasped for air and struggled to breathe.

The most high-profile of the three executions happened in Oklahoma, when Clayton Lockett, who had been convicted of murder and other charges, had what one witness called a “violent reaction” during his lethal injection. Lockett strained, grimaced and clenched his jaw; the execution was called off, and he was declared dead 43 minutes later. While most executions in the United States pass with little public notice or comment, Lockett’s prompted criticism from then-President Barack Obama and the United Nations. It was also among those cited by Sotomayor in her dissent.

“Science and experience are now revealing that, at least with respect to midazolam-centered protocols, prisoners executed by lethal injection are suffering horrifying deaths beneath a ‘medically sterile aura of peace,'” Sotomayor wrote Tuesday.

A state investigation later blamed problems in Lockett’s execution with the IV insertion. Oklahoma resumed lethal injections eight months later, though state officials would later admit that they used the wrong drug in the January 2015 execution and almost used an incorrect drug in another that year. Executions in Oklahoma were halted when the Supreme Court agreed to hear a challenge to the state’s lethal injection protocols (the justices upheld the procedure), and they were further postponed after the episodes with the wrong execution drugs. They have not resumed.

Further reading:

Sotomayor questions whether lethal injection is ‘our most cruel experiment yet’

Justices Breyer and Ginsburg: ‘It is highly likely’ the death penalty is unconstitutional

Florida Supreme Court says hundreds of death row inmates may get new sentences and avoid execution

Lethal injection drugs are scarce. Arizona wants its death row inmates to bring their own.

The recent history of states scrambling to keep using lethal injections

Supreme Court Justice Breyer: California embodies the death penalty’s ‘fundamental defects’