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'We are going backward': How the justice system ignores science in the pursuit of convictions

Forensic techniques including bite-mark comparisons and blood-spatter analysis have sent dozens of innocent people to prison.
Law enforcement authorities continue to rely on methods that researchers have called dubious, saying forensic examiners’ experience and intuition should not be discounted.
Law enforcement authorities continue to rely on methods that researchers have called dubious, saying forensic examiners’ experience and intuition should not be discounted.Eleni Kalorkoti for NBC News

When Paul Aaron Ross returns to court for a new trial in the 2004 murder of a 26-year-old woman, prosecutors will rely on bite marks to prove that he did it — even though the technique has been discredited by dozens of scientists and multiple studies.

Judges have said bite-mark evidence is fine to present, and in American courtrooms, that is what matters ─ not the mounting body of research questioning bite marks’ reliability, or the list of people convicted on such evidence only to be exonerated later.

Across the country, forensic techniques found tenuous by independent researchers representing a variety of specialties — including linking indentations found on a victim’s body to a suspect’s teeth — are still being used as evidence to convict people.

And that, critics say, can lead to wrongful convictions.

“If we don’t have technologies that are objective, repeatable and reliable, then we have no idea how many times we’re making the wrong decision,” said Alicia Carriquiry, director of the Center for Statistics and Applications in Forensic Evidence, a government-funded project to measure the limits of forensic methods. “We don’t even have a way to estimate how many times we’re making the wrong decisions.”

Over the past decade, dozens of studies have warned of the inaccuracy of commonly used methods of forensic science.

Some of the methods, including bite-mark comparisons and blood-spatter analysis, are now considered by many researchers to be scientifically dubious, responsible for dozens of wrongful convictions and deserving no place in the criminal justice system.

Others, such as shoe prints, fingerprints and ballistics comparisons, can still be useful, the researchers say, but only with the caveat that they do not provide definitive answers.

However, law enforcement authorities continue to rely on these methods, saying forensic examiners’ experience and intuition should not be discounted. Judges, meanwhile, are wary of bucking prior rulings, choosing to accept the methods as they always have rather than risk failed prosecutions.

There is no way to precisely measure how often a particular technique is used, or to say exactly how many people have been wrongfully convicted because of its use.

The National Registry of Exonerations has documented 553 cases since 1989 in which someone was convicted on false or misleading forensic evidence and later cleared. The growing list of exonerations includes a Texas man whose 1987 murder conviction, based on bite-mark evidence, was thrown out in December, and an Illinois man declared innocent in January in the retrial of a murder case that hinged on dubious ballistics evidence.

But the exonerations likely represent only a fraction of the cases in which faulty forensics sent innocent people to prison, researchers say.

“People continue to be exonerated, and we still see the courts let it in,” said Brandon Garrett, a Duke University Law School professor.

Patrick Pursley
Patrick Pursley was acquitted of murder in January 2019 after he challenged ballistics evidence used to convict him two decades earlier. Ivan Moreno / AP file

In 2018, two men in Ohio, including a former police sergeant, lost their appeals after being convicted of murder with the help of bite-mark evidence. Blood-spatter evidence ─ which the National Academy of Sciences says is plagued with “enormous” uncertainties ─ was used in murder cases in Seattle and New Mexico in 2018 and in North Carolina in 2017, and was upheld on appeal in 2018 in an Ohio assault case. Men in Tennessee and Pennsylvania were convicted of murder last year based, in part, on shoe-print evidence, which government researchers have said is not dependable enough to match to a particular shoe or person.

The divide between science and justice has widened in the nearly two years since the Justice Department under then-Attorney General Jeff Sessions ended an Obama-era partnership with independent scientists to improve forensics. In 2017, Sessions disbanded the National Commission on Forensic Science, which included researchers, scientists, lawyers, evidence examiners and law enforcement officials, and replaced it with a Forensic Science Working Group, which is housed within the Justice Department and is led by a career prosecutor.

Sessions stepped down in November, but others in the Trump Justice Department share his view that scientists should not have oversight of how forensic techniques are used by law enforcement. They include Deputy Attorney General Rod Rosenstein, who complained in August that “forensic science has been under attack” by critics who took “an erroneously narrow view of the nature of science and its application to forensic evidence.”

The critics — scientists, defense attorneys, those who investigate wrongful convictions — say such moves have slowed the momentum to abandon questionable forensics and bring courtrooms into the 21st century.

“We are going backward,” said Betty Layne DesPortes, a criminal defense lawyer in Virginia and former president of the American Academy of Forensic Sciences, a professional association of forensic examiners and lawyers. “We need to get past the trust-me phase and get us to the show-us phase, because that’s what science is supposed to be ─ based not on faith, but on results.”


A little after noon on June 24, 2004, a fisherman on Canoe Creek Lake in Blair County, Pennsylvania, found the bound, beaten and sexually abused body of Tina Miller near a boat launch. Suspicion focused on Ross, who’d been with Miller nearby the night before.

There were no witnesses to the killing, leaving authorities to build a case on circumstantial evidence: a man who said he had dropped Miller and Ross off near the boat launch, former girlfriends who said he’d abused them, a mark found on one of Miller’s breasts, and items collected from the scene ─ including a shoe print and a beer bottle. None of it definitively linked Ross to the murder, and Ross denied killing Miller, asserting that another man had picked her up in a truck. But prosecutors argued that, taken collectively, the evidence proved his guilt.

He went to trial in 2005, and a bite-mark examiner helped seal his conviction.

The examiner, Dr. Dennis Asen, was a dentist with 25 years of experience identifying bodies by their teeth and examining bite marks. On the stand, he recalled viewing Miller’s body at the morgue and concluding that her breast bore patterns of a bite mark. He took a photograph of it and made an “overlay tracing” that he uploaded to a computer and compared with molds of Ross’ teeth and the teeth of four other suspects, including three who’d been in contact with Miller in the hours before her death. Asen said he found the mark “very highly consistent” only with Ross’ teeth. Asen acknowledged, however, that he couldn’t say with 100 percent certainty that Ross had made the mark. The defense hired its own bite-mark examiner, who said he was unable to determine whether Ross left the mark.

Ross was convicted of first-degree murder and sentenced to life in prison. But the conviction was overturned by an appeals court that ruled the trial court had “abused its discretion” in refusing to give Ross’ lawyer more time to prepare, and allowing the former girlfriends’ testimony. Prosecutors plan to try Ross again, but the process has stalled amid a battle over the bite-mark evidence.

Defense lawyers, including members of the New York-based Innocence Project, have cited government reports and academic studies, including from the National Academy of Sciences, the President's Council of Advisors on Science and Technology and the Texas Forensic Science Commission. The reports have shown that no one has sufficiently proven that human bite marks are unique, or that skin is a reliable material to record them ─ or that forensic dentists can reliably identify a human bite mark in the first place.

"This is evidence...that has been accepted for 40 or 50 years."

“Today there is absolutely no way for us to know how often a forensic dentist is right and how often he is wrong,” Dana Delger, an Innocence Project lawyer, told Blair County Judge Jolene Kopriva at a pre-trial hearing for Ross in 2016.

The county’s district attorney, Richard A. Consiglio, has defended bite-mark evidence, saying the authors of scientific reports lack “real world” experience. He has pointed out that no court in any state has ruled against admitting it.

“This is evidence, your honor, that has been accepted for 40 or 50 years, not quite as old as I am, but 40 or 50 years, maybe longer, accepted by courts everywhere,” Consiglio told Kopriva in 2016.

The judge sided with prosecutors.

“Although the use of bite-mark evidence is beginning to face challenges, it would be premature for this court to order that the methodology is no longer generally accepted in the relevant scientific community,” Kopriva wrote in March 2017.

The Innocence Project responded with a blog post — since deleted — that described the case as an example of “willful scientific illiteracy among the judiciary.” Kopriva imposed a gag order preventing either side from talking publicly about the case outside of court.

Ross’ attorneys appealed Kopriva’s decision to the Pennsylvania Supreme Court, which in November sent it back to a lower court to decide, a process that could take months.

Ross, who has been in state prison for more than 13 years, did not respond to written requests for comment; his lawyers, citing the gag order, advised him not to speak.


Just after midnight on Christmas Eve in 2006, Brad Jennings called police in Texas County, Missouri, to report that he’d found his wife, Lisa, dead of a gunshot wound to the head, his revolver under her body. He told investigators they had fought the night before, and he believed she had taken her life. The local coroner and law enforcement authorities agreed, listing suicide as the cause of death.

A few months later, Lisa Jennings’ younger sister contacted the Missouri State Highway Patrol and said she believed Brad had killed Lisa. Sgt. Dan Nash began looking through the crime-scene photos and was drawn to an image of Lisa’s right hand. On it was a single drop of blood.

Nash later acknowledged in court that at the time he had little formal training in blood-spatter analysis. It’s a method of reconstructing a crime by looking at the shape and pattern of blood left at the scene, including the speed and direction blood travels and how that changes depending on the type of injury, the victim’s final movements and the victim’s proximity to a shooter. The National Academy of Sciences has described “enormous” uncertainties about the technique, and the Texas Forensic Science Commission has raised “serious questions” about the education and training of blood-pattern examiners.

This photo from the scene of Lisa Jennings' death fueled an investigator's suspicion that she hadn't taken her own life.
This photo from the scene of Lisa Jennings' death fueled an investigator's suspicion that she hadn't taken her own life.Crime scene photo

The drop of blood made Nash suspicious: If Lisa had held the gun in her right hand, why wasn’t there more blood on it?

That question became central to a new investigation that viewed Jennings not as a grieving widower but as a murder suspect.

Jennings denied shooting his wife. He turned over to police a bathrobe and slippers he was wearing that night. Analysts found Lisa’s blood. Jennings explained that it had gotten on the robe when he held her body after finding her dead.

But Nash also said the blood on the robe fit the characteristics of “blowback” from a nearby gunshot.

Nash concluded Lisa had been murdered, and he laid out his case at Jennings’ 2009 murder trial, which ended with a conviction. Jennings was sentenced to 25 years in prison.

Six years into the sentence, a lawyer working on Jennings’ behalf discovered evidence that authorities had failed to share with his defense team: tests that turned up no traces of gunshot residue on Jennings’ robe ─ undercutting the assertion that he had pulled the trigger.

In 2016, Jennings’ lawyers asked for the conviction to be thrown out. That request prompted a round of legal arguments that brought new scrutiny on the original blood-spatter analysis.

Jennings’ lawyers hired Joseph Slemko, a 30-year Canadian police officer and longtime bloodstain pattern analyst. Slemko examined the crime-scene photos and concluded that the blood patterns did not indicate that Jennings had killed his wife. He cited research showing Nash had been wrong to assume Lisa’s hand should have had more blood on it. It was “clearly a suicide,” Slemko said.

Jennings’ conviction was thrown out in February 2018, and prosecutors decided not to try him again.

“It’s been a while, but I’m sure glad to get out of there,” Jennings told reporters after his release. He said it was hard not to lose hope in prison. “You wonder sometimes if anything will ever happen. But we made it. That’s all that matters.”

Now Jennings is suing the investigators who built the case against him, saying he suffered “indescribable mental anguish” in prison.

Citing the pending litigation, Jennings’ lawyers would not let him comment. The Missouri State Highway Patrol, where Nash is still employed, declined to comment.


While critics say bite-mark and blood-spatter evidence have no place in the criminal justice system, there is also mounting scrutiny of less contentious forms of evidence — fingerprints, ballistics, shoe prints — that researchers say should be used only if authorities acknowledge their limitations.

Used correctly, these “pattern matching” techniques can be paired with other evidence to link a suspect to a crime — or exclude one, experts say. Used improperly, these methods can help build a case against the innocent.

In 1982, a teenage couple, Annette Cooper and Todd Schultz, were murdered and dismembered in West Logan, Ohio, a small town outside Columbus. Police focused on Dale Johnston, Annette’s stepfather, who lived on a nearby farm. They suspected him of killing the couple out of jealousy.

Near the bodies, investigators found what they believed was a shoe print in mud. They sent a photograph and a casting of it to an FBI examiner, along with boots belonging to Johnston. The examiner could not determine whether the boot made the mark ─ or whether the mark was a boot print at all. He sent the specimens to a North Carolina forensic anthropologist who concluded that one of Johnston’s boots made the mark.

Investigators also found a witness who, after being hypnotized, a technique sometimes used by law enforcement to enhance memories, said he remembered seeing Johnston force the couple into a car.

Johnston insisted that he was innocent. But those two pieces of evidence turned the case against him. The FBI examiner testified at Johnston’s trial before a three-judge panel that he couldn’t find a match between his boot and the impression from the scene. But prosecutors also presented a deposition from the North Carolina anthropologist in which she said “it appears” that the heel of Johnston’s boot “could have indeed made that impression.” Johnston was convicted in 1984 and sentenced to die.

After nearly six years on death row, Johnston’s conviction was thrown out after an appeals court found that the hypnosis techniques were unreliable and that prosecutors withheld evidence that Johnston could have used in his defense. Further legal challenges led a court to find that police had seized Johnston’s boots improperly, leaving the shoe-print evidence unusable. The case fell apart, and in 1990 Johnston was freed.

Since Johnston’s exoneration, footwear analysis has been the subject of warnings from researchers, including, most recently, the National Academy of Sciences and the President's Council of Advisors on Science and Technology, which said such comparisons rely on an examiner’s subjective determination and are not supported by scientific studies.

Tom Tyack, the lawyer who represented Johnston at his original trial, said he was a victim of forensic fraud.

“I honestly believe that the whole idea that you can do this stuff and have it make sense scientifically is garbage,” he said.

Johnston left prison with virtually nothing; he and his wife divorced, she was ostracized and hospitalized for mental illness and they lost their farm, said James Owen, one of his lawyers. His younger stepdaughter was put in foster homes before eventually being placed back in her mother’s care. Both women remain traumatized, Owen said.

"What they did to me they can do to anybody."

After leaving prison, Johnston lived with his mother and eventually got remarried. But he continued to live under a cloud of suspicion until 2008, when a convicted sex offender admitted that he’d killed the couple. A second man pleaded guilty to helping dismembering the bodies.

Johnston sought compensation from authorities for his wrongful conviction, but he was repeatedly denied on legal technicalities. In December, Ohio lawmakers passed a law that could enable Johnston to finally receive a payout. But he is 85 and suffering from the early stages of dementia, a family spokesperson said. Johnston could not be reached for comment.

Former death row inmate Dale Johnston in Grove City, Ohio on March 9, 2015.
Former death row inmate Dale Johnston in Grove City, Ohio, on March 9, 2015.Andrew Welsh-Huggins / AP file

Interviewed about his ordeal in 1992, Johnson said his wrongful conviction cost him everything.

“What they did to me they can do to anybody. That’s the scary part,” Johnston told the CBS News television show “48 Hours.” “They can convict anybody that they set out to convict if they choose to abuse part of the process.”


Lots of work, and not much to show for it.

That is the story of the past decade: Researchers have repeatedly warned about the shortcomings of forensic science, forensic examiners have accused the researchers of disregarding the benefits of such methods, and the criminal justice system has resisted doing things differently.

After DNA analysis triggered a wave of exonerations that exposed many forensic methods as flawed, politicians sought advice on how to make things better. The National Academy of Sciences in a 2009 report called for an overhaul of the forensic sciences, including the creation of a federal agency with the power to oversee the work of forensic scientists and enforce national standards.

A fingerprint is enlarged for examination in the Latent Print Lab at the U.S. Homeland Security Investigation Forensic Laboratory in Tyson Corner, Virginia, in 2016.
A fingerprint is enlarged for examination in the Latent Print Lab at the U.S. Homeland Security Investigation Forensic Laboratory in Tyson Corner, Virginia, in 2016.Paul J. Richards / AFP - Getty Images file

But Congress didn’t act on it, leaving all changes voluntary and subject to the whims of state and local authorities.

Then in 2013 the Obama Justice Department created the National Commission on Forensic Science, an advisory panel that aimed to pick up where the National Academy of Sciences left off. Its recommendations, too, were voluntary.

“There was a lot more talk than action mostly because we didn’t get the independent agency,” said Suzanne Bell, who sat on the commission and chairs West Virginia University’s Department of Forensic and Investigative Science.

Obama then asked his Council of Advisors on Science and Technology to investigate. The result was a 2016 report that drew public attention back to the issue, repeating many of the concerns raised by the National Academy of Sciences seven years earlier.

But the recommendations faced resistance from the Department of Justice under Obama. The FBI accused researchers of making “broad, unsupported assertions” and of making unscientific judgments itself. Then-Attorney General Loretta Lynch said her agency would reject the council’s conclusions.

"Forensic science is under attack."

In 2017, under President Donald Trump, the Justice Department disbanded the National Forensic Science Commission altogether. In its place, then-Attorney General Sessions named a former state prosecutor to head a new Forensic Science Working Group with a more limited mission: coming up with “uniform language” for federal experts’ testimony.

William Fitzpatrick, the district attorney in Onondaga County, New York, who is a member of the New York Forensic Science Commission, said he welcomed more research but was wary of losing the ability to use bite-mark and blood-spatter evidence, which remained useful despite being marred by inexperienced examiners. Fitzpatrick said he was even more concerned about attempts to undermine the validity of “tried and true” methods like fingerprint and ballistics comparisons.

“Part of the story is how forensic science is under attack, and it’s fair to say, yes, and sometimes for good reason,” Fitzpatrick said. “But I think more generally that prosecutors are under attack.”

Karen Kafadar, a co-director of the Center for Statistics and Applications in Forensic Evidence, said the reform effort isn’t meant to undermine solid cases.

“But when evidence is presented with shockingly little probability, I think it would be wise for people to be very cautious,” Kafadar said.

There have been scattered attempts to improve forensic science, and some examiners have started changing the way they testify, describing the limits of how certain they can be that evidence points to a suspect, researchers say.

However, Kafadar said, “for the most part, things haven’t changed much.”