A recent pair of botched executions has renewed the debate over lethal injection and whether it’s actually less inhumane than other methods used to execute condemned prisoners.

In January, when Ohio used a new drug “cocktail” to execute convicted rapist and murderer Dennis McGuire, he reportedly gasped repeatedly and took more than 25 minutes to die. Days earlier, when Oklahoma executed Michael Lee Wilson, the convicted killer uttered these last words: “I feel my whole body burning.”

Leaving aside the issue of whether the death penalty itself is inhumane, one might think that science could be enlisted to help devise a method of execution that spares the condemned from needless suffering.

Certainly there are historical examples of scientists and physicians offering their execution expertise. In the late 19th Century, researchers in the U.S. developed the electric chair as a more humane alternative to public hangings. Despite their efforts, executions using the chair often proved to be quite grotesque. As U.S. Supreme Court Justice William Brennan wrote in a dissent to the Supreme Court in the case of Glass v. Louisiana (1985):

The prisoner’s eyeballs sometimes pop out and rest on [his] cheeks. The prisoner often defecates, urinates, and vomits blood and drool. The body turns bright red as its temperature rises, and the prisoner’s flesh swells and his skin stretches to the point of breaking. Sometimes the prisoner catches on fire … Witnesses hear a loud and sustained sound like bacon frying, and the sickly sweet smell of burning flesh permeates the chamber.

Roughly a century earlier, French physicians Joseph-Ignace Guillotin and Antoine Lois developed the guillotine to be a painless and efficient execution machine.

In any case, many doctors today are guided by the Hippocratic Oath, which forbids them from willfully inflicting harm on others.

“It is unethical for physicians (the only ones with the requisite knowledge) to participate in the unwilling demise of any human being,” Dr. David Lubarsky, anUniversity of Miami anesthesiologist who has conducted research on lethal injection, told The Huffington Post in an email. “We don’t kill people who want to live. We don’t help others kill people who want to live… Once you cross the line as an agent/enabler of the state to cause the death of someone not seeking to die, you are no longer a healer.”

When lethal injection got its start in 1977, the medical community certainly kept its distance.

As Deborah Denno, a Fordham University law professor who has testified in many lethal injection cases, said of the invention of the three-drug protocol typically used in lethal injection, “There was no medical testing of the drug combination. There was no science. I think it was the pretense of science and a medical veneer. It was basically concocted in an afternoon.”

Now, in some states, critical drug shortages have forced corrections departments to find new untested drug alternatives.

“It’s not like you have a scientific expert sitting there and saying ‘these are the drugs you should use and in this amount.’” Denno said. “To the contrary I think one of the reasons we see these constant problems and this jump from drug to drug is these people, either they’re getting no advice whatsoever or the advice they’re getting is very bad and it’s all under the table.”

Even if science could aid in the development of a more humane killing method, Denno said, those with the appropriate expertise are unlikely to get involved.

“In light of a long-standing history from the late 1800s up to the present time, I would be extraordinarily surprised if the scientific community ever got involved in this issue.”

Keep reading for a look at methods of execution in use at various times.