Forensic Psychology Chapter 4 PDF

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Forensic Psychology: Chapter 4 Trace Evidence in Context  Forensic identification o Links physical evidence to a suspect; usually involves comparison between two samples  Trace evidence o Includes fragments of physical evidence left at or transported from a crime scene  Biometrics o Identifies suspects based on measurable anatomic traits Measures and Meaning in Forensic Identification  Evidence from crime scene matched to evidence from suspect o Source attribution: common source match o Inclusion: substantially similar match o Individuation: match excludes all other possibilities o Exclusion: matches substantially inconsistent o Inconclusive: evidence incomplete or contaminated Communicating the Nature and Certainty of a Match  Ways forensic identification experts communicate their findings o Qualitative statement: involves subjective, non-statistical statement of a match strength o Simple match: matches shares characteristics o Match plus statistics: include statistics to determine how rare or common; places match in context o Individuation: indicates detailed and perfect match Scientific Foundations of Forensic Identification: Definitions  Measures must be reliable and valid  Reliability: consistency or repeatability of a measure or observation o Test-retest reliability (temporal consistency): high if a measure yields the same results over time o Inter-rate reliability (inter-observer agreement): degree to which two or more observers or analysts independently arrive at the same measurement  Validity: technique measures what it is supposed to measure Scientific Foundations of Forensic Identification  DNA history o 1953: Watson and Crick published a seminal (A Structure for Deoxyribose Nucleic) o Late 1980s: Jefferys and colleagues recognize forensic potential of DNA o 1988: DNA introduced as evidence in U.S. courts (People v. Wesley) o CODIS maintained by FBI as largest, most frequently used DNA database in world

Forensic Psychology: Chapter 4

How is DNA evidence produced? o DNA is extracted and analyzed from biological evidence using computerized measuring instruments o Genetic profiles are detected and displayed as alleles on a DNA strand and graphed o When two profiles match, a random match probability (RMP) is calculated to estimate probability that match could occur by chance o An Imperfect DNA relies on the subjective judgment of the analyst which raises error risk o RMPs are presented to judge or jury during trial Scientific Foundations of Forensic Identification  And so: DNA identification o Reliable and valid method o Most objective o Solid scientific foundation o Some limitations  Fingerprint history o 1892: Galton introduces fingerprinting as a method of identification o Turn of century: others developed detailed classifications for fingerprints  How is fingerprint evidence produced? o Fingerprint features: friction ridges, latent prints, minutiae o Fingerprint lifted from crime scene and computer analyzed to determine potential match o Human examiner sorts matches and makes final judgment  Error source o Print quality poor o Examiner error exists o One dissimilarity doctrine ignored o Commonness or rarity of specific ridge characteristics not addressed  Bifurcations: single ridge splits into two  Ends: ridge stops  Crossovers: two ridges joined by a bridging ridge  Independence: short ridges with clear end points  For fingerprint identification o Less objective o Based on judgment of examiner o Subjective o Influenced by cognitive biases 

Forensic Psychology: Chapter 4 o Confirmation bias o Several limitations SCIENTIFIC AMERICAN SPOTLIGHT  Can DNA Analysis yield police-style sketches of suspects? o First sequencing of a complete human genome using ancient DNA recently completed o DNA alone provides fewer clues than whole cells o Continued research into alternative genetic markers for forensic use o Acceptance in forensic field not yet achieved Identification Techniques of Weak or Unknown Validity  Bullet Mark Analysis o Fell out of favor with court in 2004 o National Research Council Study findings o No striation standards o Bullets from same box could be extremely similar or dissimilar in chemical profiles  Bite Marks Analysis o Six degrees of certainty o Inconclusive o Suspect not source o Improbable suspect not source o Possible suspect is source o Probably suspect is source o Source attribution to reasonable medical certainty o ABFO  Tool Signature Identification o Trace unsuitable for microscopic comparison o Trace eliminates tool as source o Some agreement between trace and source o Identification o AFTME Reducing Error and Bias in Forensic Identification  Ensuring proper handling of trace evidence  Retesting of trace evidence on routine basis  Utilizing blind and double-blind testing  Designating evidence as property of legal system  Requiring extensive experience and graduate training in science for forensic psychologists Jurors and Trace Evidence

Forensic Psychology: Chapter 4 Jurors have difficulties interpreting probability/statistical statements Some statements cue more exemplars (exemplar theory) Jurors often have limited understanding of scientific foundation of forensic identification Jurors are more persuaded by fingerprint evidence and often believe fingerprint identification is a science Remaining Fundamental Problems  Weak scientific foundation for many forms of trace evidence  Risk of contamination or misinterpretation of the trace evidence  How the strength of a “match” or near match is communicated to a jury or judge    ...