The state of Virginia executed its first female killer since 1912 on Thursday. After putting Teresa Lewis to death by lethal injection, officials shipped her body to the medical examiner for autopsy. Why would you bother to do an autopsy on someone who was executed?
Mostly to make sure the anesthetic worked. A lethal injection comprises a cocktail of drugs designed to bring about a painless death via anesthesia, paralysis, and cardiac arrest. If the anesthesia fails, however, the prisoner feels a torturous burning sensation as a lethal dose of potassium chloride enters her bloodstream. The paralysis makes matters worse, since the condemned cannot scream or signal to the executioners that she is in distress. Unless someone monitors the inmate's brain waves, which some states have tried, the best way to assess the state of anesthesia is by measuring the concentration of anesthetic in the inmate's blood after death. Studies on human volunteers have shown that a concentration of around 20 mg of thiopental per liter of blood would be significantly higher than you'd need to perform surgery. There may be some variation in how effective the anesthetic is—the stress of being executed can increase requirements, and a prisoner's past drug use might make her exceptionally tolerant to the anesthetic. But, as a general rule, blood concentrations above 20 mg/L strongly suggest that the prisoner passed away without pain.
Unfortunately, most states wait so long to conduct the exam that the results have little value. Blood thiopental concentration drops precipitously after death, and most experts believe you'd need to draw a sample within an hour of passing to know whether the dose was adequate. Few states move that quickly. Even medical examiners who go to the prison rather than waiting for the body to arrive at the morgue rarely get a sample in less than an hour. Perhaps as a result, the autopsy data suggest that the anesthetic is often ineffective. A 2005 paper used these delayed analyses to estimate that 43 percent of inmates suffer through their injections. (The study summoned a storm of opposition.)
Medical examiners do more than draw blood from an executed prisoner. They also examine the site where the intravenous needles were inserted to confirm that they were placed appropriately. Most examiners also check for internal injuries—a sign that someone beat up the prisoner before the execution.
The validity of the drug-dose testing isn't the only source of controversy. Some states have tried to autopsy executed prisoners over the objections of family members. In December 2009, Tennessee executed Cecil Johnson, then tried to conduct an autopsy even though he had signed an affidavit arguing that it would violate his Baptist faith. Johnson's body remained in limbo for more than a month, until the state courts prohibited the autopsy.
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Explainer thanks Mark Dershwitz of the University of Massachusetts Medical School and Adele Lewis of Forensic Medical Management Services. Thanks also to reader Andy Brownstein for asking the question.