History
U.S. Navy odontologist cataloging dental remains.
Prior to the early 1970s, forensic odontologists largely limited their work to efforts related to identifying victims of natural or human-caused disasters. The discipline had refrained from applying its methods in criminal prosecutions over concerns regarding the difference between identifying mass disaster victims using complete dentition with the goal of identifying and distinguishing remains and identifying the source of a bite mark left in skin. Crime scene bite marks contain a small fraction of the information available from the full dentition of disaster victims, and the information that is available from bite marks is not reliable — skin is elastic and can be distorted at the time of and after the bite. Some experts found exceptions to this general rule and began to identify bite marks they deemed unusual and well-defined.
One of the first seminal cases in which bite mark comparison evidence was accepted into the trial record was in California. In People v. Marx (1975), three dentists testified at trial that the laceration on the victim’s face came from an unknown set of teeth that were “indistinguishably similar” to the teeth of the man on trial. The defense challenged the admissibility of the experts’ testimony, arguing that their testimony was “novel and not generally accepted by the field of odontology” and thus inadmissible under California’s Kelly-Frye test, and that it violated a previously established doctrine. The trial court ultimately allowed the bite mark comparison evidence to be admitted, and Mr. Marx was convicted.
In 1978, the California Court of Appeals definitively ruled that bite mark identification met the standard of general scientific acceptance, basing this decision on the testimony of three expert forensic odontologists in Marx. The establishment of the Daubert standard in 1993, which requires scientific validity for admissible evidence, did not significantly impact the admissibility of bite mark evidence in court.
No court has broadly ruled that bite mark evidence or expert testimony is categorically inadmissible in legal proceedings, however this evidence has been used in more than two dozen wrongful convictions across the U.S.
Standards of Care
The American Board of Forensic Odontology (ABFO) published guidelines in 1984 that describe the best practices and procedures for collecting evidence from both victims and suspects. To begin the collection process, forensic odontologists must record demographics, the location of the bite mark(s), the shape of the bite, the color and size of the mark, and the type of injury (i.e., puncture or bruise). The odontologist must also photograph the evidence from a variety of perspectives, in both color and black and white imaging, both with and without flash, closeup images for 1:1 scale, and UV photography if it is an older injury. Bite marks should be swabbed to determine whether DNA remains on the skin from the individual who left the bite mark(s). If the bite mark resulted in a puncture wound, the odontologist is expected to make an impression of the bite mark for analysis. The ABFO provides several conclusions that odontologists can reach in their initial review of the evidence: exclusion (not a bite mark), possible bite mark (pattern may or may not be caused by other factors, but cannot rule out biting), probable bite mark (pattern suggests bite mark but could be result of something else), and definite bite mark (no reasonable doubt teeth created the pattern).
Forensic odontologists must also determine whether a bite mark on a victim or object came from a human or nonhuman. Bite mark cross-sections on skin differ from species to species. The number of teeth marks, the space between the marks, and the shape are essential to this determination. Human incisors produce rectangular marks, while canine teeth produce more triangular marks. If there is a suction mark present in a bite mark, that is generally indicative of a human bite.
Forensic odontologists are responsible for swabbing any bite marks in efforts to collect transferred DNA. While some bite marks do retain foreign DNA, it is not guaranteed that a sample will contain DNA from anyone other than the victim, if the bite mark is on a human. Some scientists have hypothesized that the presence of enzymes within human saliva may break down DNA on human skin.
Concerns with Bite Mark Analysis and Forensic Odontology
Several concerns have been raised about the validity of bite mark comparison as a forensic technique. In 2009, the National Academy of Sciences’ Committee on Identifying Needs for the Forensic Science Community found that “with the exception of nuclear DNA analysis, however, no forensic method has been rigorously shown to have the capacity to consistently, and with a high degree of certainty, demonstrate a connection between evidence and a specific individual or source.”
Specifically addressing issues with forensic odontology, the Committee found that the ABFO guidelines ultimately fail to “indicate the criteria necessary for using each method to determine whether the bite mark can be related to a person’s dentition and with what degree of probability.” The Committee also noted that there has not been any thorough study with a large population “to establish the uniqueness of bite marks.” While the Committee acknowledges theoretical studies have promoted the uniqueness of bite marks, these studies “include more teeth than are seen in most bite marks submitted for comparison.” Importantly, the Committee also included, “[i]f a bite mark is compared to a dental case using the guidelines of the ABFO, and the suspect providing the dental case cannot be eliminated as a person who could have made the bite, there is no established science indicating what percentage of the population or subgroup of the population could also have produced the bite.” In an ABFO analysis of 100 cases by 39 separate analysts, there were just four instances where the analysts could agree that the bite mark was that of a human being. Without this ability to exclude people by both characteristics and statistics, “a threshold of evidentiary value has not been established.”
Case Studies
According to a 2020 article from the Innocence Project, at least 26 people have been wrongfully convicted based on bite mark evidence. Of those 26 individuals, 6 were sentenced to death (23%).
Ray Krone
A December 29, 1991, murder at CBS Lounge in Phoenix, Arizona would become a landmark case surrounding forensic bite mark analysis. The victim was discovered naked and stabbed to death in the men’s bathroom, her clothes scattered about. The crime scene yielded several pieces of evidence: footprints on the floor, a missing kitchen knife, and two bite marks — one on the victim’s breast and another on her neck. While saliva was collected from the victim’s body, it only revealed a common blood type, and other DNA testing proved inconclusive. With no eyewitnesses to the crime, investigators turned their attention to Ray Krone, a regular patron who was supposed to help close the bar the previous night.
Mr. Krone had no criminal record, had graduated in the top 10% of his high school class, and served honorably in the U.S. Air Force, achieving the rank of sergeant. At the time of the murder, he had been working as a letter carrier for the U.S. Postal Service for seven years. His connection to the victim was minimal — they occasionally played darts together, and he had once driven her to a Christmas party. When police asked Mr. Krone to bite into a piece of Styrofoam at the police station, he complied.
The case against Mr. Krone hinged primarily on bite mark comparison. Dr. John Piakis, a local dentist serving as the Forensic Odontologist for the Maricopa County Medical Examiner’s Office, examined the bite marks and the Styrofoam impression and concluded that Mr. Krone’s notably crooked teeth matched the bite mark on the victim’s breast. Dr. Piakis went so far as to claim that “only someone with a snaggletooth, like Krone, could have made that mark.” Two days after the murder, police arrested Mr. Krone, charging him with murder, kidnapping, and sexual assault. The media dubbed Mr. Krone the “Snaggletooth Killer.”
During his 1992 trial, Mr. Krone maintained his innocence and claimed he had never gone to the bar the night before the murder. However, Dr. Raymond Rawson testified for the prosecution that the bite marks on the victim’s body “absolutely” matched the impressions that Mr. Krone left on the Styrofoam at the police station. He told the jury that “a match is not 90% or 99% a match 100% there is no other possibility.” Dr. Rawson also produced a video to demonstrate his techniques and claimed that bite mark comparison was more reliable than other methods, saying “it’s not if bite mark evidence is as good as fingerprints, it’s if fingerprints are as good as bite marks!” The judge found three aggravating circumstances warranting the death penalty: the especially heinous nature of the crime, the bite mark mutilation suggesting debasement, and the shocking nature of the murder compared to typical first-degree murders. Mr. Krone was sentenced to death.
Bite mark evidence used in Ray Krone’s case
Four years later, in 1996, Mr. Krone won a new trial on appeal and was once again sentenced to death. The prosecution again relied heavily on the bite mark comparison evidence, however, the judge expressed significant doubt about Mr. Krone’s guilt and instead sentenced him to life in prison rather than death, noting that the case would “haunt me for the rest of my life.” It was not until 2002 that DNA testing of saliva found on the victim’s clothing excluded Mr. Krone as a possible contributor and matched Kenneth Phillips, who was already incarcerated for an unrelated sex crime. At the time of the murder, Mr. Phillips lived near the bar where the victim was killed. Notably, Mr. Phillips did not have crooked teeth or a snaggletooth, undermining Dr. Rawson’s testimony.
In April 2002, after serving ten years in prison, Mr. Krone was released, and prosecutors dismissed all charges against him a month later. Mr. Krone was the 100th person to be exonerated from death row since 1976 and the 12th death row prisoner whose innocence was proven through DNA testing. The case against Ray Krone became a powerful illustration of the unreliability of bite mark comparison and led the American Board of Forensic Odontology (ABFO) to change its guidelines to limit the use of certainty statements like those made by Dr. Rawson.
Sources
Alissa Bjerkhoel and Hon Christopher J. Plourd, The Death Row Case of Ray Krone, the Beginning of the End of Bite Mark Evidence in the United States, Journal of the California Dental Association, 2023; Saks, M. J., Albright, T., Bohan, T. L., Bierer, B. E., Bowers, C. M., Bush, M. A., Bush, P. J., Casadevall, A., Cole, S. A., Denton, M. B., Diamond, S. S., Dioso-Villa, R., Epstein, J., Faigman, D., Faigman, L., Fienberg, S. E., Garrett, B. L., Giannelli, P. C., Greely, H. T., Imwinkelried, E., … Zumwalt, R. E, Forensic bitemark identification: weak foundations, exaggerated claims, Journal of Law and the Biosciences, 2016; Bhargava & Bhargava, et al., An Overview of Bite mark Analysis, Journal of Indian Academy of Forensic Medicine, 2012; National Research Council, Strengthening Forensic Science in the United States: A Path Forward, The National Academies Press, 2009.