Forensic dentistry is predicated on the idea that a person's bite is as unique as a person's fingerprint, and that the human body can accurately record that distinct pattern. In other words, bite someone hard enough while committing a crime in the US, and that bite mark can be used to tie you to the crime.
Though the viability of bite mark evidence has regularly been challenged by both legal experts and forensic scientists — in 2009, the National Academy of Sciences released a report warning that there was very little scientific basis to bite analysis — the evidence has been readily permitted in US courtrooms for 50 years. But on Friday, in a first, the Texas Forensic Science Commission (FSC) voted to recommend a moratorium on bite mark evidence in criminal cases until further research can establish whether or not it's reliable.
The decision comes after a five-month investigation of the integrity of bite mark analyses, which was done at the urging of The Innocence Project, a nonprofit legal organization committed to exonerating the wrongfully convicted. FSC is now conducting an audit of all Texas convictions that have hinged on bite mark evidence.
The repercussions of FSC's conclusions are expected to be huge, and set a precedent for other states nationwide.
"This will reverberate throughout the legal and scientific community," said Chris Fabricant, director of strategic litigation at the Innocence Project. "It's been entirely discredited."
Fabricant estimates that hundreds if not thousands of convictions around the country have been driven or compounded by bite mark evidence. He can't estimate how many of those convictions are potentially wrongful, but he does say that the fact forensic dentistry was permitted in courts for so long is "an outrage" and "a total failure" of the justice system. Dozens of suspects who were convicted by bite mark evidence have later been exonerated through the use of DNA. Many of those exonerees were facing the death sentence.
When medical examiners are confronted with an apparent homicide, they might call a forensic pathologist to figure out how the person was killed. If the victim's body has noticeable bite marks on it, the forensic pathologist might summon a forensic dentist to photograph the injury. The dentist then uses those photographs to draw conclusions about the width, depth, and orientation of each tooth in the assailant's mouth. Prosecution teams call forensic dentists to the stand to compare moldings of a suspect's teeth with the bite mark.
'It's not unique, like a fingerprint. Any number of people could fit in a given bite mark.'
"Lay jurors and lay courts accepted conclusions that were urged by experts on the stand," Fabricant said. "Experts who showed up with an impressive and imposing army of instruments… were given a cloak of science by the court, and were therefore given great weight by jurors."
When Steven Mark Chaney was charged with murdering East Dallas couple John and Sally Sweek in 1987, nine witnesses corroborated his alibi. But in the end, that didn't matter. One juror later said that it was the bite mark analysis that convinced her of Chaney's guilt above all else, and he was sentenced to life behind bars.
Chaney was exonerated last October when state district judge Dominique Collins agreed with Chaney's attorneys that the bite mark comparisons linking him to the crime were fundamentally unsound. After the hearing, Judge Collins gave Chaney a slice of pumpkin pie and stepped down from the bench to shake his hand. Chaney walked out of the Dallas courtroom a free man after 28 years in prison.
Dr. Jim Hales, chief dental consultant for the Dallas County Medical Examiner's Office and a board-certified forensic dentist, testified as one of the two expert dentists at Chaney's trial in 1989. Hales testified that he had examined bite marks on John Sweek's arms with his own eyes. He presented more than 15 photos of the marks to the jury, along with plaster and wax dental impressions of Chaney's teeth, and said he'd spent 20 hours comparing the impressions and the marks. Hales testified that "both the upper and lower arches" of Chaney's mouth "were consistent with" and "matched" the bite marks left on Sweek's arm, according to court documents. Hales also noted that "the spacing between the appellant's teeth and the spacing in the bite marks were 'very much' consistent."
Hales concluded with "reasonable dental certainty" that there was a "1 [in] a million" chance that someone other than Chaney was responsible.
Twenty-eight years later, however, Hales wasn't so certain of those odds. In an affidavit, he wrote that what he told jurors back in 1989 was no longer valid.
"Conclusions that a particular individual is the biter and their dentition [the way teeth are arranged in the mouth] is a match when you are dealing with an open population are now understood to be scientifically unsound," Hales wrote.
Mary and Peter Bush are a married couple who lead a team of researchers in the forensics department at the University at Buffalo. They began questioning bite mark analyses in 2007.
The Bushes set out to test the two fundamentals of bite mark analyses — the uniqueness of human dentition and that human skin can accurately record bite marks. They were the first scientific research team to substantively challenge the methodology of the practice, and the first to conduct research using human cadavers as opposed to animal matter.
They found absolutely no evidence supporting the notion that human dental arrangements are in any way unique.
"It's not reliable," Peter Bush said. "We carried out a number of experiments and found that the wrong dentition sometimes fit the bite than the one that made it…. We had one study where we looked at 1,100 specimens and had a number of matches. It's not unique, like a fingerprint. Any number of people could fit in a given bite mark."
Nor did they find any evidence supporting the claim that human skin can preserve and record bite marks with any degree of accuracy. Their research made them pariahs in the world of forensic science.
"We've had quite severe negative reactions," Peter Bush said. "We've been personally attacked, heckled at national conferences."
Bite mark analysis was first challenged more than 300 years ago in Salem, Massachusetts. In 1692, Reverend George Burroughs was arrested on suspicion of witchcraft. Bite marks were found on some of the girls he was suspected of trying to recruit; at the trial, the prosecution opened Burroughs' mouth and "compared his teeth with the teeth marks left on the bodies of several injured girls in the courtroom." Burroughs was convicted and hanged.
Months after Burroughs was hanged, the governor of Massachusetts called for an end to the witch trials, and voiced his concern that "spectral and intangible evidence" was being used in criminal courts. Burroughs' conviction was overturned 20 years after his execution.
But by the 1950s, bit mark analysis was again being used in US courtrooms.
However, even some critics of the way bit mark evidence is used say that it does have the potential to serve a purpose in trials.
"If done properly, it can help exonerate the innocent and convict the guilty," said Haskell Pitluck, a retired Illinois judge and former president of the American Academy of Forensic Sciences. "However, the problem I've mentioned for years is that there are too many people who try to do too much with too little."
Pitluck, who now serves as the legal advisor to the American Board of Forensic Odontology, says that bite mark analyses can help eliminate innocents from a group of suspects. For example, if the dental arrangement recorded in a bite mark injury matches one suspect out of three, then that match can help narrow the focus of an investigation.
"We've come a long way," Pitluck said. "Some of the cases may have been wrong — I would hate to say that any of them were on purpose, but anyone can make a mistake."
Mistakes in the criminal justice system, however, can have devastating consequences.
"I'm ready to face the absence of it in court rather than risk it being used in the wrong way," Richard Alpert, assistant criminal district attorney for the Tarrant County District Attorney's Office and member of the Texas Forensic Science Commission, told the Dallas Morning News on Thursday.
Chris Fabricant from the Innocence Project expects that the FSC's determinations will encourage other states to review the practice of bite mark analysis with similar scrutiny, which could give hope to people convicted on bite mark evidence who maintain their innocence. People like Eddie Lee Howard, 61, who was sentenced to death in 1992 for the rape and murder of a Mississippi woman. The only physical evidence linking Howard to Kemp was the supposed match between the bite mark injuries on the victim, which were recorded after the body was exhumed, and impressions of his teeth.
The Mississippi Supreme Court concluded in 2000 that the evidence was solid. However, last summer, the Court granted Howard's appeal for a retrial. Attorneys from the Mississippi Innocence Project will present new evidence relating to his case, including new DNA, and the original bite mark evidence will be reviewed.
Follow Tess Owen on Twitter: @misstessowen