In 2017, as lawyers for prisoners in Ohio sought to spare their clients from lethal injection, they challenged one of the state’s key witnesses: Daniel Buffington.

As he had done elsewhere, the Florida-based pharmacist had submitted written testimony saying that prisoners would not feel pain from the three-drug cocktail administered by executioners. But the lawyers for the men on death row argued that Buffington was unqualified to testify in an upcoming hearing, noting that he had not administered general anesthesia or conducted research on midazolam, the key sedative in the execution protocol.

U.S. Magistrate Judge Michael Merz denied the motion to bar Buffington’s testimony. And when prisoners’ lawyers challenged the pharmacist again in court, the judge stood his ground.

“He’s certainly better able to understand and explain induction of anesthesia than I am,” the judge said of Buffington. “I have no experience of induction of anesthesia except having had anesthesia induced on my own body and watching it with my wife and my son, and that’s far less than this witness has.”

Merz admitted Buffington as an expert witness in that proceeding and considered his testimony.

Legal experts say such exchanges illustrate a critical weakness in the judicial system: While the law relies in part on lawyers to scrutinize experts, judges must also evaluate a host of technical issues for themselves, weighing questions like whether a forensic technique is legitimate science or whether a particular drug will anesthetize a prisoner. And some experts say jurists are not always well equipped to do so.

“It’s very, very hard,” Patrick Schiltz, the chief U.S. district judge for the District Court of Minnesota, said in a telephone interview. Schiltz is also the chair of the advisory committee on evidence rules for the Judicial Conference of the United States, the governing body of the federal court system.

Before 1993, judges had to decide only if the testimony of an expert was consistent with generally accepted methodologies in the field. That year, though, the Supreme Court issued a landmark decision in the case Daubert v. Merrell Dow Pharmaceuticals Inc., setting a new standard for federal jurists evaluating scientific testimony. The ruling instructed federal judges to rigorously scrutinize the science directly, considering factors like whether the expert’s theory had undergone peer review. Six years later, in a 1999 ruling, the court strengthened judges’ gatekeeping power by applying the standard to all expert witnesses, not just those giving scientific testimony.

Together, these mandates presented a significant challenge for judges, particularly in the arena of capital punishment and lethal injection, where debates often involve complex and evolving science.

“Sometimes we have really, really hard technical issues,” Schiltz said. “And it is a criticism of Daubert that it asks the judges to do something that judges aren’t particularly well suited to do.”

Jules Epstein, a professor at Temple University’s law school, was more blunt. “A courtroom is a really lousy place to decide science,” he said.

Complicating matters is the fact that a significant portion of the judiciary has inconsistently applied the rules for admitting expert witnesses. Federal judges are supposed to act as gatekeepers that consider whether there’s more than a 50% chance that the expert’s opinion is reliable, a standard known as the preponderance of the evidence. But one recent study of more than 1,000 federal court opinions determining the admissibility of expert testimony in 2020 found that in 13% of cases, the standard for admissibility used was less stringent than the law demands, and judges actually presumed that the expert’s testimony would be admissible.

In bench trials, which take place in front of a judge instead of a jury, judges also can allow experts to testify, then decide later how much weight to give their testimony. This has happened at least twice in method of execution cases where states have hired Buffington.

A judge’s initial decision on an expert witness can have far-reaching consequences. Legal experts told ProPublica and Type Investigations that jurists look to what other judges decided in past cases when they are weighing an expert’s qualifications. “Being admitted once as an expert essentially guarantees acceptance going forward,” Chris Fabricant, the director of strategic litigation at the Innocence Project, wrote in an email.

As ProPublica and Type have reported, seven states have hired Buffington to vouch for their execution protocols since 2015, when he first appeared in a lethal injection case. Judges have allowed him to testify in nearly every instance, with the exception of the Ohio case, where Merz later excluded him. Even then, it was not due to his qualifications but because he did not list his prior expert testimony in a way that complied with federal rules. (Merz declined to comment on the case, saying the court’s practice is not to speak about past decisions. Buffington has said in court that opposing counsel took issue with the formatting of his disclosure form. “That information wasn’t conveyed in time to reformat the form,” Buffington testified in Arkansas in 2019. “We were working on that, but the judge made the decision that there was a time threshold and precluded on that.”)

Buffington declined to be interviewed about the findings of the ProPublica-Type investigation, but a spokesperson for the pharmacist said Buffington has significant training and professional expertise in the areas of his testimony, including pharmacology and toxicology, and has held positions over the years in various medical organizations, including the American Medical Association and the American Pharmacists Association. “Dr. Buffington’s pharmacology training and professional experience make him well qualified to provide expert opinions on medicines and their effects in a wide range of areas,” the spokesperson wrote. “The core training, curriculum and clinical practice experience within the Doctor of Pharmacy degree and practice of pharmacy is centered on the domain of pharmacology.”

The spokesperson also dismissed the criticism by prisoners’ experts. Disagreement between expert witnesses, the spokesperson said, “is a hallmark of the American justice system. It is expected and utterly unremarkable that for every case in which Dr. Buffington served as an expert witness, the opposing side will disagree with his testimony.”

In cases unrelated to lethal injection, however, some judges have also challenged Buffington’s credentials, criticizing him for crafting what they considered to be thinly researched opinions and for attempting to testify beyond the scope of his expertise.

In 2018, for instance, a judge found him unqualified to testify as an expert in a case brought by the widow of a veteran accusing the Department of Veterans Affairs of negligence in her husband’s death. “Dr. Buffington is not competent to testify regarding the standard of care — or breach thereof — by medical doctors, nurses, osteopathic physicians, or physician’s assistants, as these are different professions from that of a pharmacist,” wrote Judge James Randal Hall, chief U.S. District Court judge for Georgia’s Southern District. (Neither Hall’s office nor Buffington responded to requests for comment about the ruling.)

In another case, a judge scoffed at Buffington’s work, which he said lacked sufficient evidence or analysis to back up the pharmacist’s conclusions. “Buffington’s opinion is entirely without any intellectual rigor or any indicia of reliability,” wrote U.S. Magistrate Judge Mark Lane, who in 2017 excluded Buffington’s testimony in a case about regulatory compliance for a medication guide. (A spokesperson for Buffington said Buffington “testified to specific FDA guidelines” and the judge’s statement “contradicted the FDA’s established requirements.”)

The Judicial Conference has recognized a need to clarify the rules for judges. Last year, it proposed amendments to the Federal Rules of Evidence, clarifying language to underscore the responsibility that judges have to be gatekeepers of expert testimony. The amendments will go into effect in December 2023 if the Supreme Court adopts them and Congress does not reject them.