Forensic Science: Uniqueness Controversy

Uniqueness in Forensics: Fact or Fiction

• Recent criticisms question the uniqueness of forensic features, particularly highlighted in the 2009 National Academy of Sciences report.
• The report emphasizes that reliability in forensic disciplines cannot solely rely on claims of uniqueness.
• Proving individualization in forensic science remains contested and methodologically flawed, questioning its validity.

Evidence for Uniqueness

• Anecdotal evidence and experience, based on subjective memory and inductive reasoning, are unreliable indicators of uniqueness.
• Historical failures, such as blood-letting and phrenology, demonstrate the unreliability of inductive reasoning.
• Even with rare traits, duplicates may exist; mathematical analysis suggests a high probability of encountering a duplicate after observing one.
• The formation process of friction ridge and dental patterns is assumed unique due to random forces, but no studies verify these forces are infinite.
• Small sample sizes and flawed statistical models weaken claims of uniqueness for fingerprints, dental traits, and toolmarks.
• Most studies do not verify assumptions with real-world data, reducing the strength of conclusions on uniqueness.

Quantification of Uniqueness

• Even calculating a very low probability of a match doesn't prove uniqueness; probability models still allow for duplicates.
• The assumption that probabilities can be rounded to zero without empirical validation is a logical flaw.

Logic and Interpretation of Studies

• Many studies misinterpret their findings as proving uniqueness.
• Even if differences in traits between identical twins are observed, this doesn't prove uniqueness across populations.
• The claim of dentition's uniqueness is a reader's interpretation, not the authors'; the authors only conclude identical twins are not identical.

Twin Studies

• Twin studies focus on trait heritability, not proving uniqueness.
• Differences between identical twins are attributed to non-genetic factors.
• These studies do not establish uniqueness but show similarities.

Firearms and Bullets Analysis

• Claims that no two barrels leave identical marks are supported by studies proving consecutively rifled barrels leave different marks but not that marks are unique.

Uniqueness as a Cultural Ideology

• Uniqueness is historically linked to religious and philosophical beliefs.
• The concept persists in modern beliefs about nature's variations.

Relevance to Forensic Practice

• Forensic analysis focuses on the probability of a match rather than proving uniqueness.
• Unique characteristics may exist, but they are not central to forensic methods.

Irrelevance of Uniqueness in the Legal System

• The error rate in forensic analysis is more critical than the concept of uniqueness to the legal system.
• Judges and legal systems prioritize accuracy and reliability in forensic evidence, not claims of uniqueness.
• Terms like "individualization" are used instead of "uniqueness," but still involve assumptions of uniqueness.

Resource Allocation in Forensic Research

• Proving uniqueness diverts resources from quantifying match probabilities and improving forensic methods.
• The pursuit of uniqueness is philosophical, not a practical objective.

PCAST: Objective vs. Subjective Methods

• Objective methods utilize standardized, quantifiable procedures with minimal human judgment.
• Subjective methods rely heavily on human judgment and are more susceptible to bias, inconsistency, and error.

PCAST: Foundational Validity Requirements

• Reproducible, consistent procedures are required for identifying, comparing features, and determining matches.
• Empirical measurements of false positive rates and sensitivity are necessary to assess accuracy.
• Black-box studies assess examiner performance by measuring identification accuracy or errors.

PCAST: Key Points

• Subjective methods can be vulnerable to examiner bias and inconsistency in forensic analysis.
• Human judgment in subjective methods creates a "black box" for scientific assessment.
• Black-box studies measure multiple examiners and evaluate their error rates for forensic methods.
• Empirical validation is crucial for forensic methods.
• Two metrics—false positive rate and sensitivity—evaluate a method's accuracy.

PCAST: Foundational Validity

• Foundational validity ensures reliability in principle.
• Validity as applied means reliable method application in practice.
• Legal requirement: Experts must reliably apply the method to the case facts.
• Critical criteria (validity as applied): Examiner capability, measuring correctness, availability for review, scientifically valid probability of chance occurrences, reporting false positive rates and random match probabilities.
• Claims should align with empirical evidence and valid statistical principles.

PCAST: Proficiency Testing

• Proficiency testing empirically evaluates analyst performance and capability.
• Proficiency testing types include assessing protocol adherence and skill improvement exercises.

PCAST: Non-Empirical Views

• "Theories" of identification in forensic science are often circular and lack empirical support.

PCAST: Empirical Views

• Forensic science shows increasing application of objective measures of accuracy.
• Examples include fingerprint identification, toolmark evidence, bitemark evidence, latent print examiners, and forensic neuroimaging.

Kaufman Report Summary: Chapter II: Forensic Evidence

• The evidence presented in the Christine Jessop case focused on physical contact, transport, and potential cause of death, using forensic science findings.

Kaufman Report Summary: Hair Findings

• A dark hair (necklace hair) found on Christine's body was microscopically similar to Guy Paul Morin's.
• Subsequent findings of similar hairs from classmates undermine initial findings.

Kaufman Report Summary: Value and Misuse of Hair Evidence

• Hair comparison lacks strong probative value without DNA analysis.
• The evidence linking Morin's hairs and the scene was not conclusive.

Kaufman Report Summary: Early Findings and Communication

• Preliminary hair comparison influenced interpretations and possibly police actions.
• Testimony about the findings may have been inaccurate, creating a misinterpretation of the evidence.

Kaufman Report Summary: Chapter V: Investigation and Prosecution

• Christine Jessop's body was discovered in Durham Region on December 31, 1984.
• Insufficient search coverage, especially in darkness, is a detail.
• Found smoking paraphernalia near a non-smoker suspect.

Kaufman Report Summary: Guy Paul Morin

• Initial suspicion of Morin was based on community observation.
• Early interviews with Morin may have been influenced by initial suspicions.

Kaufman Report Summary: Interview Process

• Lack of thorough record-keeping and selective taping for interviews hindered reliability.

Kaufman Report Summary: Arrest

• Morin was arrested on April 22, 1985.

Kaufman Report Summary: Leslie Chipman

• Chipman's testimony, later admitted to be false, was influenced by authorities.

Kaufman Report Summary: Mandy Patterson

• Patterson's testimony was based on personal feelings rather than factual evidence.

Kaufman Report Summary: Morin and Evidence of Guilt

• Morin’s lack of specific actions (searching, attending funeral, expressing condolence) was argued as evidence of guilt.
• The Inquiry ruled this irrelevant for lack of probative value.

Kaufman Report Summary: Alibi Defense and Crown Conduct

• Morin’s alibi defense was challenged.
• Potential biases by the Crown hinder objectivity; their initial assumptions affected evidence assessment.

Kaufman Report Summary: Insanity Defense

• An insanity defense was proposed during the first trial, based on the basis of schizophrenia.
• Prosecutors remained convinced of Morin’s guilt, influencing evidence interpretation.

Kaufman Report Summary: Stay Motion and Disclosure

• Defence sought a stay due to non-disclosure of evidence.
• Some disclosure errors were acknowledged, but no malice was found.
• Some evidence disclosure failures occurred from the police.