The triple-drug cocktail used by many states to kill death-row inmates may not always provide a painless death. Will moving to a new method quiet criticism?
On 1 August 2012, Ronald Smith was supposed to die.
He was sentenced to death by the state of Montana for two murders he committed more than 30 years ago. But, after three decades on death row and several planned and postponed execution dates, a new legal challenge caused yet another delay.
This challenge is not linked to the crimes for which Smith was convicted; it is about the method the state plans to use to end his life.
The American Civil Liberties Union (ACLU), which brought the case, claims the three-drug protocol that Montana uses in executions could cause unnecessary suffering.
Designed by anaesthesiologist Stanley Deutsch as an "extremely humane" way to end life, it is supposed to work quickly and painlessly.
But recent cases of apparently painful three-drug executions have triggered a debate about the value of this method.
Since it was first used in Texas in 1982, the triple-drug cocktail, as it is known, has become the standard execution method in the US.
The first drug, a barbiturate, "shuts down" the central nervous system, rendering the prisoner unconscious.
The second paralyses the muscles and stops the person breathing. The third, potassium chloride, stops the heart.
The three-drug method was presented as a more humane replacement for lethal gas and the electric chair.
But critics are sceptical.
"It's impossible to fully understand what these drugs do to people," says Deborah Denno, a professor of law at Fordham University in New York.
"They may be too sedated [by the first drug] to cry out, or in pain but paralysed, or locked in, by the second drug."
The 14 December 2006 execution of inmate Angel Diaz in Florida took a total of 34 minutes, and a second round of injections to complete.
Witnesses to the execution reported that Diaz "gasped" and "grimaced" during the procedure.
An autopsy revealed chemical burns on Diaz's arms, where needles had been pushed all the way through veins and into soft tissue.
Jeb Bush, Florida's governor at the time, temporarily suspended state executions the following day.
A paper later stated that the inmate probably died from "progressive suffocation" caused by the nerve-blocking drug, and that he was likely to have experienced "potassium-induced sensation of burning".
The team of lawyers and medical experts who wrote the paper concluded: "The conventional view of lethal injection leading to an invariably peaceful and painless death is questionable."
In 2008, the US Supreme Court ruled that the triple-drug protocol was indeed lawful and did not violate the eighth amendment to the US constitution, which forbids "cruel and unusual punishment".
But in 2009, after a two-hour attempt to execute Rommel Broom via a triple-drug cocktail, Ohio became the first state to change its procedure to a single dose of anaesthetic.
Technicians were unable to find a suitable vein to administer the drugs. After 18 jabs, he was released back to death row, where he remains today.
After Ohio, other states followed suit.
While 24 out of 33 states that have the death penalty still use the three-drug protocol, five states have now used a single-drug method, and four have announced their intention to switch to one-drug lethal injections.
"In the last two years, we've seen more changes in the drug protocol than in the entire history of lethal injection," Prof Denno says.
States that have made the change have been quiet about their reasons.
Explaining its own recent decision to change from a three-drug to a single-drug protocol, the Georgia Department of Corrections would only say to the BBC that it had reviewed "medical testimony, and met with corrections officials around the US" to discuss its execution procedures before making the decision.
The switch also comes as states face shortages of the drugs needed for the three-drug cocktails. The European Union, where most of the drugs are manufactured, has placed export restrictions on medications to be used in lethal injections.
Dr Jay Chapman, who first approved the triple-drug cocktail in 1977 when he was Oklahoma's state medical examiner, has now endorsed the single drug method, which uses a single high dose of anaesthesia - the same method used to put pets to sleep.
Dr Chapman told BBC News: "A one-drug protocol is employed by veterinarians for euthanasia simply because the procedure is humane."
The one-drug method, which takes longer to end life than the three-drug system, was not considered when lethal injection was first devised. The slower time was seen as less humane.
Austin Sarat, a professor of jurisprudence at Amherst College in Massachusetts says that lethal injection, like electrocution, hanging and lethal gas before it, has been shown to have "flawed technology" that prevents the guarantee of a painless death every time.
"In hanging, this means people were strangled rather than having their necks broken," he says. "There have been cases where people [in the electric chair] burst into flames.
"Three drugs didn't do it, now we're at one. We need to kill people softly, to kill people gently in order to have a legitimate form of execution. And we just can't figure out what that is."
But Dr Chapman thinks that the current methods are indeed humane.
"Considering the method by which these people despatched their victims, it's perhaps a little too humane," he says.
Additional research by Karen Millington