Documentation, collection, and preservation of DNA evidence

Bitemark Examinations:

• The Claim: Bitemark analysis purports to match a bite mark found on a victim or at a crime scene to the unique dental characteristics of a suspect. The underlying assumption is that human dentition is unique enough to allow for individualization, similar to fingerprints.
• Why it’s Considered Junk Science:
  • Lack of Uniqueness: Unlike fingerprints, the scientific premise that human dentition is unique to the point of positive individualization has not been empirically validated. Studies have shown significant similarities between different individuals’ teeth.
  • Distortion and Variability: Bite marks left on skin are highly susceptible to distortion due to factors like skin elasticity, movement of the victim, time elapsed, and the location of the bite. These distortions make accurate comparisons incredibly challenging and subjective.
  • Subjectivity of Analysis: The analysis process is often highly subjective, relying on the examiner’s interpretation of the bite mark and the suspect’s dentition. There is a lack of standardized methodologies and objective criteria for comparison, leading to inconsistent and unreliable conclusions.
  • High Error Rates: Proficiency testing and reviews of past cases have revealed alarmingly high error rates in bitemark analysis, including false identifications that have contributed to wrongful convictions.
  • Lack of Scientific Validation: The foundational research supporting the reliability and accuracy of bitemark analysis has been deemed weak and insufficient by numerous scientific bodies, including the President’s Council of Advisors on Science and Technology (PCAST) in their 2016 report on forensic science in criminal courts. PCAST concluded that bitemark analysis does not meet the scientific standards for foundational validity.
• Impact: Wrongful convictions based on flawed bitemark evidence have had devastating consequences, highlighting the unreliability of this technique.

2. Document Examinations (Specifically Handwriting Analysis for Individualization):

• The Claim: Forensic handwriting analysis aims to identify or eliminate a specific individual as the writer of a questioned document by comparing their handwriting characteristics to known samples. The underlying assumption is that each person’s handwriting is unique and consistent enough for individualization.
• Why it’s Increasingly Considered Junk Science:
  • Lack of Demonstrated Uniqueness: While handwriting exhibits individual variations, the claim that these variations are unique to a degree that allows for absolute individualization has not been scientifically established through robust studies with known error rates.
  • Intra-Writer Variability: An individual’s handwriting can vary significantly depending on factors like writing instrument, writing surface, emotional state, and the passage of time. This intra-writer variability can make accurate comparisons challenging.
  • Subjectivity of Interpretation: The analysis often relies on the examiner’s subjective interpretation of handwriting features and their significance. Standardized objective criteria for determining a match or non-match are often lacking.
  • Limited Error Rate Studies: While some studies have attempted to assess error rates, they often suffer from methodological limitations and do not provide a clear understanding of the real-world reliability of the technique. PCAST found that while feature comparison methods for handwriting are likely valid for some purposes, claims of individualization and error rates beyond a certain level are not scientifically supported.
  • Cognitive Bias: Examiners can be susceptible to cognitive biases, especially when they are aware of other evidence in the case or have a preconceived notion of the writer’s identity.
• Clarification: It’s important to note that document examination encompasses more than just handwriting analysis. Examiners also analyze paper, ink, printing processes, and alterations, some of which have a stronger scientific basis. The “junk science” label primarily applies to the individualization of handwriting to a specific writer with a high degree of certainty.

3. Microscopic Hair Examinations:

• The Claim: Microscopic hair comparison involves examining the morphological characteristics of hairs found at a crime scene and comparing them to hairs from a known individual. Examiners look at features like color, diameter, shape, and the presence or absence of a medulla. The goal was often to associate a questioned hair with a specific individual.
• Why it’s Now Considered Junk Science:
  • Lack of Demonstrated Uniqueness: Microscopic hair characteristics are not unique to a specific individual. Different people can share similar microscopic hair features, and even hairs from the same individual can vary. Therefore, a microscopic match cannot definitively identify a single source.
  • Subjectivity of Analysis: The comparison process is highly subjective, relying on the examiner’s visual assessment and interpretation of the similarities and differences between hairs. There are no standardized objective criteria for determining a match.
  • High Error Rates and Overstatements: Studies and reviews of past cases have revealed that microscopic hair examiners frequently overstated the significance of a match, claiming associations that were not scientifically supported. The FBI, for example, conducted a review of thousands of cases and found that examiners made erroneous statements in over 90% of microscopic hair comparison cases.
  • Advantage of DNA Analysis: The advent of nuclear and mitochondrial DNA analysis of hair has provided a far more scientifically reliable and discriminatory method for hair comparison. DNA analysis can often definitively include or exclude an individual as a source, highlighting the limitations and unreliability of relying solely on microscopic characteristics.
  • PCAST Conclusion: PCAST concluded that microscopic hair analysis is not scientifically valid for identification and should only be used for exclusion purposes or as a preliminary screening tool.
• Impact: Numerous wrongful convictions were based, in part, on overstated or erroneous microscopic hair comparison testimony. These exonerations underscore the fundamental flaws in relying on this technique for individualization.

Conclusion:

Bitemark analysis, handwriting analysis for individualization, and microscopic hair examinations have all faced significant scientific scrutiny due to a lack of robust foundational validity, subjective methodologies, high error rates, and the availability of more reliable scientific methods (particularly DNA analysis). While document examination beyond handwriting individualization has some valid aspects, the overreliance on subjective interpretation in these three areas has led to their increasing categorization as “junk science.” The legal and scientific communities are now more aware of the limitations of these techniques, emphasizing the need for rigorous scientific validation, standardized procedures, and transparent reporting of limitations and error rates in forensic science disciplines. This shift aims to prevent wrongful convictions and ensure that forensic evidence presented in court is reliable and scientifically sound.