When junk science decides guilt in the South

• States should adopt the federal standard for expert testimony and make reliability a threshold requirement, not a question left for jurors to sort out after unreliable science has been heard.

In an American courtroom, few words carry more weight than “the science shows.” 

Jurors may question an eyewitness or a defendant’s explanation, but forensic evidence is different. When someone dubbed “an expert” testifies about forensic evidence, such testimony carries substantial weight. However, bite marks, hair comparisons, bloodstain patterns, and other analyses have turned out to be junk science – unvetted, inaccurate, and unreliable. When the State fails to act as gatekeepers, so-called ‘expert testimony’ is mistaken for scientific proof.

Under modern evidentiary standards, scientific analysis should not reach a jury unless it rests on reliable methods and validations. Yet for decades, courts admitted forensic disciplines before their reliability had been established. For example, bite-mark analysis, microscopic hair comparison, and bloodstain interpretation was presented to juries as objective science, even though unbiased researchers had failed to validate their reliability. The consequences were devastating—innocent people were convicted, guilty people remained free, and public trust in the criminal justice system eroded.

Those harms have been especially severe in the South because junk science did not operate in a vacuum. It operated alongside underfunded public-defense systems, elected coroners with limited medical training, and communities where Black defendants often faced judges, juries, prosecutors, police departments, and forensic witnesses shaped by the region’s racial past. A forensic claim that might have been challenged by a well-funded defense team could become nearly unanswerable for a poor defendant in a rural county.

The clearest example is Mississippi. In The Cadaver King and the Country Dentist, Radley Balko and Tucker Carrington write about how the state’s criminal justice system allowed forensic pathologist Dr. Steven Hayne and bite-mark analyst Dr. Michael West to become two of its most influential expert witnesses. For years, Hayne performed the bulk of Mississippi’s criminal autopsies, while West repeatedly testified, untruthfully as it turns out, that bite marks could identify suspects with remarkable precision.

Their influence mattered because Mississippi’s death-investigation system was not merely inefficient; it was historically tied to local politics. Like many Southern states, Mississippi relies heavily on county-level officials and informal arrangements rather than a consistently independent, professionally staffed medical examiner system. In such an environment, Hayne and West often testified as neutral experts, but in reality, they were peddling junk science as part of the prosecution’s team. 

The human cost was enormous. Levon Brooks and Kennedy Brewer, two Black men from rural Mississippi, were convicted in separate child-murder cases after testimony from Hayne and West link them to bite marks that later proved unreliable. Together, they spent decades in prison before DNA evidence exposed the truth: another man was responsible. Their cases show how junk science can do more than convict the innocent. It can protect the guilty by giving the legal system a false sense of certainty.

The tragedy is not only that two so-called experts got it wrong. It is that judges repeatedly allowed juries to hear testimony that lacked the scientific foundation Courts accepted their testimony with little scrutiny because it sounded scientific and because the defendants most harmed by it often lacked the money, status, and institutional trust needed to challenge it. In the South, where criminal punishment has long been entangled with racial politics, that failure carries particular weight.

The problem with junk science isn’t limited to Mississippi courtrooms. Just last month, the Louisiana Supreme court freed a man on death row who was convicted using bite mark analysis, finding that the evidence was “scientifically indefensible.” Across the country, courts admitted forensic evidence that had never undergone the rigorous testing expected of legitimate scientific disciplines. In 2009, the National Academy of Sciences warned that many commonly used forensic methods lacked the necessary scientific support and called for major reforms. In 2016, the President’s Council of Advisors on Science and Technology reached a similar conclusion, finding that feature-comparison disciplines like bite mark and hair comparison analyses, lacked “foundational validity.” Those findings raise an obvious question: if these methods weren’t trustworthy, why were juries allowed to consider them as scientific evidence at all?

The federal government has also acknowledged the consequences of placing too much faith in junk science. In 2015, after an extensive review of microscopic hair comparison testimony, the FBI admitted that its examiners had overstated forensic conclusions in the overwhelming majority of cases reviewed, including cases involving death sentences.

These were not harmless technical errors. They helped convict real people. According to the Innocence Project, misapplied forensic science has contributed to more than half of its wrongful-conviction cases. In many of those cases, juries heard testimony that exceeded what science could actually prove. Experts offered conclusions with unwarranted certainty. But such opinions were based on techniques that had never been validated.

In the South, those errors often reinforced patterns that were already familiar: poor defendants against the state, Black defendants before institutions built during or after segregation, and rural communities dependent on local officials whose authority was rarely questioned. Phony forensics gave the system a language of certainty. It allowed prosecutors to present weak cases as scientific fact, and it made racial and class bias harder to see because the prejudice arrived wearing the mask of expertise.

There has been some progress. Courts are increasingly skeptical of opinion disguised as science. The 2023 amendments to Federal Rule of Evidence 702 reaffirmed that judges, not juries, must determine whether expert testimony satisfies reliability requirements before it is admitted. Yet too many states reject the federal approach. Mississippi is already considering changing court rules to embrace the federal approach. The state Supreme court is studying the matter. For there to be justice, the court should adopt the change as soon as possible and allow for appeals in cases where junk science and phony forensics were used.

Science deserves its privileged place in the courtroom, but only when it is truly scientific. The most important safeguard against junk science is not a better jury instruction or a stronger cross-examination. It is a judge willing to keep unreliable opinions out of the courtroom altogether. Expert testimony must be grounded in methods that have been rigorously tested, independently validated, and honestly presented to juries with their limitations fully acknowledged.

The Cadaver King and the Country Dentist is more than the story of two discredited experts. It is a warning about what happens when a legal system shaped by racial history grants scientific authority before science has earned it. In the South, the fight against junk science is also a fight against the legacy of racial discrimination in the courtroom. Every wrongful conviction based on unreliable forensics is a reminder that justice depends not only on finding the guilty, but on ensuring that the evidence used to convict is worthy of the trust placed in it.

The solution is simple. States should adopt the federal standard for expert testimony and make reliability a threshold requirement, not a question left for jurors to sort out after unreliable science has been heard. Federal Rule of Evidence 702 permits expert testimony only when it is the product of reliable principles and scientific methods rather than conjecture and opinion. States should adopt the federal approach so that evidence is not admitted because it sounds scientific; it is admitted because it is reliable.