On June 20, 1987, ... the bodies of John and Sally Sweek [were found] in their apartment. Their throats were slashed, and they had been stabbed multiple times. Police also found what they believed to be a human bitemark on John's left forearm. There were no eyewitnesses to the offense. ...
The final piece of the State's case was testimony from two forensic odontologists that a mark found on John's left forearm was a human bitemark made by Chaney at the time of the murders. ... Doctor James Hales said that there was only a "[o]ne to a million" chance that someone other than Chaney bit John because the mark was a "perfect match" with "no discrepancies" and "no inconsistencies." He claimed that the "one to a million" statistic was found in "the literature." He also testified that the injury was inflicted at the time of the murders. ... Doctor Homer Campbell, testified that the mark was actually at least four separate human bitemarks and that, after comparing dentition models and examining photographs, he was certain to a "reasonable degree of dental certainty" that Chaney was the one who bit John. The bitemark evidence was the State's strongest evidence according to its own closing arguments. ...
The defense called two witnesses to testify about the mark on John's left forearm. ... Linda Norton, testified that the mark was a human bitemark but that it was "virtually unsuitable for making a good dental comparison . . . ." because "almost anyone who has relatively even top and bottom teeth is going to be capable of leaving this bite mark." According to her, she would not have submitted the mark for comparison. ... Doctor John McDowell, a forensic odontologist, agreed with the State's experts that the mark on John's left forearm was a human bitemark, and he agreed that the photographs from Weiner's office were of good quality, but his comparisons were nonetheless inconclusive. ...
The rest of the defense's closing argument focused on discrediting the State's bitemark evidence. The defense argued that the bitemark should have been better preserved and that better equipment should have been used to examine the mark. It also asserted that bitemark comparisons are merely "interpretative," pointing to the conflicting testimony about whether the injury was even a bitemark. ...
The State spent almost all its second summation discussing the bitemark evidence. The prosecutor emphasized Hales's testimony that "only one in a million could have possibly made that bite mark" before asking the jury "[w]hat more do you need?" He then cited Campbell's testimony that he was sure, to a "reasonable degree of dental certainty," that Chaney bit John. The State also tried to discredit Norton, one of the defense experts, as a charlatan somewhere between "Quincy and Matt Dillon" and painted McDowell's testimony ... as helpful to the State even though he testified that his comparisons were inconclusive. The prosecutor concluded by arguing that the bitemark evidence was "better than eyewitness testimony. [Eyewitnesses] can make mistakes, as [defense counsel] said" and that,
In 2013, the legislature enacted Article 11.073 of the Texas Code of Criminal Procedure, which allows a defendant to obtain post-conviction relief based on a change in science relied on by the State at trial. ...
In its agreed findings of facts and conclusions of law, the habeas court found that
To support his "change in the body of the science" arguments, Chaney cites (1) excerpts from the 2009 National Academy of Science: "Strengthening Forensic Science in the United States: A Path Forward" (NAS Report), (2) an affidavit from Drs. Mary Bush, DDS, and Peter Bush; (3) an affidavit from Hales, who testified at trial; (4) a supplemental affidavit from Hales; (5) an odontology report written by Dr. Alastair Pretty; (6) a supplemental odontology report written by Pretty; (7) an affidavit from Pretty, (8) an affidavit from Drs. Cynthia Brzozowski, James Wood, and Anthony Cardoza (Brzozowski et al.); (9) a supplemental affidavit from Brzozowski, et al.; (10) an affidavit of Dr. Michael Baden, M.D.; and (11) an amicus curiae brief filed in the California Supreme Court, which was authored by 38 "scientists, statisticians, and law-and-science scholars and practitioners."
In response to Chaney's writ application, the State "acknowledges and concedes that the science behind forensic odontology, as it relates to bite mark comparison, has considerably evolved since the time of trial in 1987" and that "[u]nder today's scientific standards, Dr. Hales relayed that he 'would not, and could not' testify as he did at trial, nor could he testify that there was a 'one to a million' chance that anyone other than [Chaney] was the source of the bite mark." The State succinctly summarizes its position, when it states that "the bitemark evidence, which once appeared proof positive of . . . Chaney's guilt, no longer proves anything."
The dual principles underlying Hales's and Campbell's opinions were that a human dentition, like a fingerprint, is unique and that human skin is a medium capable of recording a person's biting surface with sufficient fidelity that a particular individual can be identified as the source of a particular bitemark. If either of those premises are invalid, then the comparisons by Hales and Campbell claiming that Chaney was a "match" have no probative value because they are based on principles now known to be unsupported by science. According to Chaney (and his experts), although those two assumptions were accepted by the scientific community at the time of Chaney's trial, that community now rejects them. He argues that experts in the field have developed a new body of science, mainly in response to the NAS Report. That report also asserted that those principles were unproven and unreliable. That report concluded that:
...
The Bushes undertook a number of peer-reviewed studies to test the assumptions underlying Hales's and Campbell's testimony. The first group of studies tried to replicate the Rawson Study's conclusion—the literature relied on by Hales and Campbell at trial—that each human dentition is unique. The Rawson Study "examined tooth positions within dentitions and concluded that the very large number of possible positions meant that the human dentition is unique 'beyond any reasonable doubt.'" However, that study was based on two unproven assumptions, according to the Bushes. The first was that there was "no correlation of tooth position (i.e., that the position of one tooth did not affect the position of any other)," and second was that "there was a uniform or equal distribution over all possible tooth positions (i.e., that tooth locations did not gather into common patterns)." Using Rawson's methods, the Bushes plotted "landmark points on two sets of dentitions, resulting in x, y, and angle coordinates for each tooth." They then looked for matches one, two, three, four, five, and six teeth at a time. They ran two thousand simulated tests to verify their results and to determine whether the Rawson Study's results would remain accurate "if its assumptions about the lack of correlation and non-uniformity of dental arrangement were ignored." Their results were contrary to those of the Rawson Study—the Bushes observed "significant correlations and non-uniform distributions of tooth positions in [their] data sets." In other words, they found that the human dentition is not unique.
In a second series of peer-reviewed studies, the Bushes devised another way to test the unique-dentition theory. They studied "dental shape in large populations using geometric morphometric analysis and mathematical modeling methods common in other scientific disciplines." They found that dental shape matches occurred in the populations that they studied, which was consistent with the results of their earlier studies and indicated that the human dentition is not unique.
The Bushes also tried to replicate the Rawson Study's conclusion that human skin can record the characteristics of a bitemark with sufficient resolution to trace the source of the bitemark to the "biter." The Bushes "began with a series of studies that used the same dentition impressed into cadavers to explore how skin might distort any marks." For example, they "examined how anisotropy might create distortion by examining bitemarks made both parallel and perpendicular to skin's tension lines (also known as Langer lines)." They also looked at the effect of tissue movement and found that "the same dentition did not produce identical marks across these conditions." Id. They found that some marks made by the same dentition were "dramatically distorted from others," and that "bitemarks created by the same dentition on the same individual appeared substantially different depending on the angle and movement of the body and whether the mark was made parallel or perpendicular to tension or Langer lines." A number of experts (and the NAS Report) agree that the human dentition is not unique and that, even if it was, skin is an inadequate medium to "match" a bitemark to a "biter."
In addition to those studies, Chaney also directs us to Hales's affidavits about his own testimony and the evolving standards of the ABFO. In his first affidavit, Hales explains that his testimony about "biters" and "matches" was acceptable at the time of trial under ABFO guidelines; however, the scientific body of knowledge about bitemark comparisons has changed since trial and that, under current guidelines, he would not, and could not, give the same opinions that he did at Chaney's 1987 trial. The habeas court reached the same conclusion, noting that the 2016 ABFO Manual has completely invalidated any population statistics, regardless of whether the population is open or closed, and that the Manual no longer allows examiners to give opinions to a "reasonable degree of dental certainty."
[W]e agree with Chaney. The body of scientific knowledge underlying the field of bitemark comparisons has evolved since his trial in a way that contradicts the scientific evidence relied on by the State at trial. New peer-reviewed studies discredit nearly all the testimony given by Hales and Campbell about the mark on John's left forearm and Chaney being a "match." The revised ABFO standards and affidavits attached to Chaney's writ application support that conclusion. ...
In his next complaint, Chaney argues that Hales's testimony that there was only a "one to a million" chance that someone other than Chaney was the source of the injury was false according to the literature at the time. He also argues that Weiner's and Hales's testimony that the bitemark was inflicted at the time of the murders was false and misleading and that the described testimony was material to his conviction. The habeas court agreed with Chaney, and we adopt the findings of fact and conclusions of law of the habeas court because they are supported by the record. ...
Even though the scientific principles at the time of Chaney's trial supported some level of individualization (although those principles are no longer credible), Hales confesses that he knew at the time of trial that the body of science did not support his "one to a million" testimony. Other record evidence supports Hales's assertions, including newly discovered notes from Hales's trial file, where he initially wrote that the odds were "thousands to one," with a nearby notation of "100,000 to 1," the Bushes's peer-reviewed studies disproving the tenets and conclusions of the Rawson Study dealing with population statistics, and the 2016 ABFO Manual forbidding the use of all population statistics. ...
The final piece of the State's case was testimony from two forensic odontologists that a mark found on John's left forearm was a human bitemark made by Chaney at the time of the murders. ... Doctor James Hales said that there was only a "[o]ne to a million" chance that someone other than Chaney bit John because the mark was a "perfect match" with "no discrepancies" and "no inconsistencies." He claimed that the "one to a million" statistic was found in "the literature." He also testified that the injury was inflicted at the time of the murders. ... Doctor Homer Campbell, testified that the mark was actually at least four separate human bitemarks and that, after comparing dentition models and examining photographs, he was certain to a "reasonable degree of dental certainty" that Chaney was the one who bit John. The bitemark evidence was the State's strongest evidence according to its own closing arguments. ...
The defense called two witnesses to testify about the mark on John's left forearm. ... Linda Norton, testified that the mark was a human bitemark but that it was "virtually unsuitable for making a good dental comparison . . . ." because "almost anyone who has relatively even top and bottom teeth is going to be capable of leaving this bite mark." According to her, she would not have submitted the mark for comparison. ... Doctor John McDowell, a forensic odontologist, agreed with the State's experts that the mark on John's left forearm was a human bitemark, and he agreed that the photographs from Weiner's office were of good quality, but his comparisons were nonetheless inconclusive. ...
The rest of the defense's closing argument focused on discrediting the State's bitemark evidence. The defense argued that the bitemark should have been better preserved and that better equipment should have been used to examine the mark. It also asserted that bitemark comparisons are merely "interpretative," pointing to the conflicting testimony about whether the injury was even a bitemark. ...
The State spent almost all its second summation discussing the bitemark evidence. The prosecutor emphasized Hales's testimony that "only one in a million could have possibly made that bite mark" before asking the jury "[w]hat more do you need?" He then cited Campbell's testimony that he was sure, to a "reasonable degree of dental certainty," that Chaney bit John. The State also tried to discredit Norton, one of the defense experts, as a charlatan somewhere between "Quincy and Matt Dillon" and painted McDowell's testimony ... as helpful to the State even though he testified that his comparisons were inconclusive. The prosecutor concluded by arguing that the bitemark evidence was "better than eyewitness testimony. [Eyewitnesses] can make mistakes, as [defense counsel] said" and that,
But, most of all, we have the bite mark. I wouldn't ask you to convict just based on the testimony of the tennis shoes, of the statements Chaney made to Westphalen, or the statements he made to Curtis Hilton. But, by golly, I'm going to ask you to convict on that dental testimony.... According to Chaney, "while much of th[e] [trial] testimony appeared to be in accord with the state of scientific knowledge in 1987 about what could and could not be concluded from a bite mark, in the intervening decades since [his] conviction, the ground on which Drs. Hales and Campbell based their assertions [about bitemark comparisons] has given way entirely." He contends that the "[s]cientific understanding about whether it is possible to 'match' a particular person to a bite mark in skin and whether random match probabilities can be given for a bite mark has now reversed course." He also argues that he is entitled to relief because Hales has changed his trial opinion that the bitemark was inflicted at the time of John's death, which was an opinion upon which the State heavily relied. Hales now believes that the wound was two to three days old when John and Sally were killed. ...
In 2013, the legislature enacted Article 11.073 of the Texas Code of Criminal Procedure, which allows a defendant to obtain post-conviction relief based on a change in science relied on by the State at trial. ...
In its agreed findings of facts and conclusions of law, the habeas court found that
no scientific evidence has been produced to support the basis of individualization of a bite mark to the exclusion of all other potential sources in an open population. [T]he reference manual published by the American Board of Forensic Odontology (ABFO) [in March 2015] ... prohibits ABFO Diplomates from testifying to individualization of bite marks in an open population, i.e., where the universe of potential suspects, or "biters," is unknown. ... Dr. Hales's use of the terms ["]match["] and ["]biter["] as it related to [Chaney] was appropriate under the ABFO guidelines and scientific field of forensic odontology at the time of trial. ... Dr. Hales's and Dr. Homer Campbell's testimony that it was their opinion, to a reasonable degree of dental certainty, that [Chaney] made the bite mark on John Sweek's arm was appropriate under the ABFO guidelines and scientific field of forensic odontology at that time. However, ... such testimony would not be justified, admissible, or accurate under today's guidelines because the scientific community and the ABFO guidelines have invalidated individualization of bite marks in an open population, as we have in this case. ... [T]he changes in science and the evolution of the field of forensic odontology as it relates to bite mark comparisons constitutes relevant scientific evidence that was not available to be offered by [Chaney] at the time of trial in 1987. As such, ... the current relevant scientific evidence related to bite marks was not available at the time of [Chaney]'s trial because the evidence was not ascertainable through the exercise of reasonable diligence by [Chaney] before the date of or during trial. ... [H]ad the bite mark evidence been presented at trial under current scientific standards, on the preponderance of the evidence [Chaney] would not have been convicted. ... [T]he [ABFO] Manual was updated again in [March 2016]. The current Manual prohibits individualization testimony entirely, regardless of whether the population at issue is open or closed. Under the current Manual, the only permissible conclusions for ABFO Diplomates are: "Excluded as Having Made the Bitemark"; "Not Excluded as Having Made the Bitemark"; or "Inconclusive." ...The record reasonably supports the findings of the habeas court, so we adopt those findings. [N]ot only has the body of scientific knowledge underlying the field of bitemark comparisons evolved in a way that discredits almost all the probabilistic bitemark evidence at trial, but also ... Hales's new opinion [is] that the bitemark was inflicted days before the murders based on his new scientific knowledge that was not available at Chaney's trial. ...
To support his "change in the body of the science" arguments, Chaney cites (1) excerpts from the 2009 National Academy of Science: "Strengthening Forensic Science in the United States: A Path Forward" (NAS Report), (2) an affidavit from Drs. Mary Bush, DDS, and Peter Bush; (3) an affidavit from Hales, who testified at trial; (4) a supplemental affidavit from Hales; (5) an odontology report written by Dr. Alastair Pretty; (6) a supplemental odontology report written by Pretty; (7) an affidavit from Pretty, (8) an affidavit from Drs. Cynthia Brzozowski, James Wood, and Anthony Cardoza (Brzozowski et al.); (9) a supplemental affidavit from Brzozowski, et al.; (10) an affidavit of Dr. Michael Baden, M.D.; and (11) an amicus curiae brief filed in the California Supreme Court, which was authored by 38 "scientists, statisticians, and law-and-science scholars and practitioners."
In response to Chaney's writ application, the State "acknowledges and concedes that the science behind forensic odontology, as it relates to bite mark comparison, has considerably evolved since the time of trial in 1987" and that "[u]nder today's scientific standards, Dr. Hales relayed that he 'would not, and could not' testify as he did at trial, nor could he testify that there was a 'one to a million' chance that anyone other than [Chaney] was the source of the bite mark." The State succinctly summarizes its position, when it states that "the bitemark evidence, which once appeared proof positive of . . . Chaney's guilt, no longer proves anything."
The dual principles underlying Hales's and Campbell's opinions were that a human dentition, like a fingerprint, is unique and that human skin is a medium capable of recording a person's biting surface with sufficient fidelity that a particular individual can be identified as the source of a particular bitemark. If either of those premises are invalid, then the comparisons by Hales and Campbell claiming that Chaney was a "match" have no probative value because they are based on principles now known to be unsupported by science. According to Chaney (and his experts), although those two assumptions were accepted by the scientific community at the time of Chaney's trial, that community now rejects them. He argues that experts in the field have developed a new body of science, mainly in response to the NAS Report. That report also asserted that those principles were unproven and unreliable. That report concluded that:
(1) The uniqueness of the human dentition has not been scientifically established.NAS Report at 175-76. It also stated that "bite marks on the skin will change over time and can be distorted by the elasticity of the skin, the unevenness of the surface bite, and swelling and healing. These features may severely limit the validity of forensic odontology." Id. at 174.
(2) The ability of the dentition, if unique, to transfer a unique pattern to human skin and the ability of the skin to maintain that uniqueness has not been scientifically established.
i. The ability to analyze and interpret the scope of extent of distortion of bite mark patterns on human skin has not been demonstrated.(3) A standard for the type, quality, and number of individual characteristics required to indicate that a bite mark has reached a threshold evidentiary value has not been established.
ii. The effect of distortion of different comparison techniques is not fully understood and therefore had not been quantified.
...
The Bushes undertook a number of peer-reviewed studies to test the assumptions underlying Hales's and Campbell's testimony. The first group of studies tried to replicate the Rawson Study's conclusion—the literature relied on by Hales and Campbell at trial—that each human dentition is unique. The Rawson Study "examined tooth positions within dentitions and concluded that the very large number of possible positions meant that the human dentition is unique 'beyond any reasonable doubt.'" However, that study was based on two unproven assumptions, according to the Bushes. The first was that there was "no correlation of tooth position (i.e., that the position of one tooth did not affect the position of any other)," and second was that "there was a uniform or equal distribution over all possible tooth positions (i.e., that tooth locations did not gather into common patterns)." Using Rawson's methods, the Bushes plotted "landmark points on two sets of dentitions, resulting in x, y, and angle coordinates for each tooth." They then looked for matches one, two, three, four, five, and six teeth at a time. They ran two thousand simulated tests to verify their results and to determine whether the Rawson Study's results would remain accurate "if its assumptions about the lack of correlation and non-uniformity of dental arrangement were ignored." Their results were contrary to those of the Rawson Study—the Bushes observed "significant correlations and non-uniform distributions of tooth positions in [their] data sets." In other words, they found that the human dentition is not unique.
In a second series of peer-reviewed studies, the Bushes devised another way to test the unique-dentition theory. They studied "dental shape in large populations using geometric morphometric analysis and mathematical modeling methods common in other scientific disciplines." They found that dental shape matches occurred in the populations that they studied, which was consistent with the results of their earlier studies and indicated that the human dentition is not unique.
The Bushes also tried to replicate the Rawson Study's conclusion that human skin can record the characteristics of a bitemark with sufficient resolution to trace the source of the bitemark to the "biter." The Bushes "began with a series of studies that used the same dentition impressed into cadavers to explore how skin might distort any marks." For example, they "examined how anisotropy might create distortion by examining bitemarks made both parallel and perpendicular to skin's tension lines (also known as Langer lines)." They also looked at the effect of tissue movement and found that "the same dentition did not produce identical marks across these conditions." Id. They found that some marks made by the same dentition were "dramatically distorted from others," and that "bitemarks created by the same dentition on the same individual appeared substantially different depending on the angle and movement of the body and whether the mark was made parallel or perpendicular to tension or Langer lines." A number of experts (and the NAS Report) agree that the human dentition is not unique and that, even if it was, skin is an inadequate medium to "match" a bitemark to a "biter."
In addition to those studies, Chaney also directs us to Hales's affidavits about his own testimony and the evolving standards of the ABFO. In his first affidavit, Hales explains that his testimony about "biters" and "matches" was acceptable at the time of trial under ABFO guidelines; however, the scientific body of knowledge about bitemark comparisons has changed since trial and that, under current guidelines, he would not, and could not, give the same opinions that he did at Chaney's 1987 trial. The habeas court reached the same conclusion, noting that the 2016 ABFO Manual has completely invalidated any population statistics, regardless of whether the population is open or closed, and that the Manual no longer allows examiners to give opinions to a "reasonable degree of dental certainty."
[W]e agree with Chaney. The body of scientific knowledge underlying the field of bitemark comparisons has evolved since his trial in a way that contradicts the scientific evidence relied on by the State at trial. New peer-reviewed studies discredit nearly all the testimony given by Hales and Campbell about the mark on John's left forearm and Chaney being a "match." The revised ABFO standards and affidavits attached to Chaney's writ application support that conclusion. ...
In his next complaint, Chaney argues that Hales's testimony that there was only a "one to a million" chance that someone other than Chaney was the source of the injury was false according to the literature at the time. He also argues that Weiner's and Hales's testimony that the bitemark was inflicted at the time of the murders was false and misleading and that the described testimony was material to his conviction. The habeas court agreed with Chaney, and we adopt the findings of fact and conclusions of law of the habeas court because they are supported by the record. ...
Even though the scientific principles at the time of Chaney's trial supported some level of individualization (although those principles are no longer credible), Hales confesses that he knew at the time of trial that the body of science did not support his "one to a million" testimony. Other record evidence supports Hales's assertions, including newly discovered notes from Hales's trial file, where he initially wrote that the odds were "thousands to one," with a nearby notation of "100,000 to 1," the Bushes's peer-reviewed studies disproving the tenets and conclusions of the Rawson Study dealing with population statistics, and the 2016 ABFO Manual forbidding the use of all population statistics. ...
Acknowledgments: Thanks to Ed Imwinkelried for calling the opinions to my attention.
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