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The Psychology of Forensic Identification Chapter 4

FORENSIC AND LEGAL PSYCHOLOGY

Mark Costanzo | Daniel Krauss | Fourth Edition

The Psychology of Forensic Identification

In this chapter

Trace Evidence in Context

When Does a Trace “Match” a Source?

Basic Principles of Scientific Measurement: Reliability and Validity

The Scientific Foundation of Forensic Identification

Techniques of Weak or Unknown Validity

FORENSIC AND LEGAL PSYCHOLOGY

Mark Costanzo | Daniel Krauss | Fourth Edition

The Psychology of Forensic Identification

In this chapter (continued)

Communicating the Similarity of a Trace and a Source

Reducing Error and Bias

Science as the Solution to the Problem of Identification Bias

How Jurors Think About Trace Evidence

FORENSIC AND LEGAL PSYCHOLOGY

Mark Costanzo | Daniel Krauss | Fourth Edition

What is forensic science?

» The collection, analysis, and interpretation of trace evidence

DNA analysis

Fingerprint analysis

Shoe print analysis

Document examination

Ballistics/firearms

Hair comparison

Bite mark comparison

Blood spatter analysis

Tool mark analysis

Tire impressions

Serology (bodily fluids)

Fire/explosive analysis

FORENSIC AND LEGAL PSYCHOLOGY

Mark Costanzo | Daniel Krauss | Fourth Edition

What is forensic identification?

» Forensic identification = the process of linking a piece of physical trace evidence to a person

» Trace evidence = evidence left at or transported from crime scene

What is physical trace evidence?

Tire prints

Sole prints

Clothing fabric

Tools marks

Fingerprints

Bite marks (victim or food)

What is biological trace evidence?

Blood

Saliva

Semen

Skin cells

FORENSIC AND LEGAL PSYCHOLOGY

Mark Costanzo | Daniel Krauss | Fourth Edition

Trace Evidence in Context

Forensic identification

Links physical evidence to a suspect; usually involves comparison between two samples

Trace evidence

Includes fragments of physical evidence left at or transported from crime scene

FORENSIC AND LEGAL PSYCHOLOGY

Mark Costanzo | Daniel Krauss | Fourth Edition

Forensic Identification Decisions

Exclusion: (exonerating)

Substantial inconsistent features (e.g., came from someone else)

Inconclusive: (not helpful either way)

Trace evidence incomplete, contaminated or impossible to analyze with precision

Source attribution: (incriminating)

Did the samples come from a common source?

Match or Inclusion: (stronger incriminating)

Features substantially similar, no substantial, unexplainable differences

Individualization: (strongest incriminating)

Came from source at exclusion of all other sources in the world

FORENSIC AND LEGAL PSYCHOLOGY

Mark Costanzo | Daniel Krauss | Fourth Edition

Strength of the Conclusion

Exclusion

Inconclusive

Source Attribution

Match

Individualization

FORENSIC AND LEGAL PSYCHOLOGY

Mark Costanzo | Daniel Krauss | Fourth Edition

How can we link trace evidence to a specific person?

» Biometrics:

identification of person based on measurable anatomical traits

Modern form: fingerprints, iris, retina, face

» Anthropometry:

Alphonse Bertillon

11 measurements

Used until 1903

Why abandoned?

FORENSIC AND LEGAL PSYCHOLOGY

Mark Costanzo | Daniel Krauss | Fourth Edition

Trace Evidence in Context

Anthropometry

Was first scientific, 11-measurement identification technique (Bertillon)

Biometrics

Identification of person based on distinctive, measurable anatomical or behavioral traits

FORENSIC AND LEGAL PSYCHOLOGY

Mark Costanzo | Daniel Krauss | Fourth Edition

Modern Biometrics: Beyond Fingerprints and DNA

Biometric identifiers: iris patterns

Face: unique facial structure

Voice: voiceprint

Signature: static and dynamic recognition

Walking: gait sequences

Technology engagement

FORENSIC AND LEGAL PSYCHOLOGY

Mark Costanzo | Daniel Krauss | Fourth Edition

See Table 4.1 for additional information

Biometrics

Includes identification of individual person based on measurable anatomical traits

Modern biometrics

Experienced rapid development due to terrorism threats and technological advancements

Can be obtained at close and far range

When Does a Trace “Match” a Source?

Many previously used forensic evidence forms found inaccurate and abandoned

Inaccurate or false assumptions about similarity or dissimilarity of evidence (e.g., bullet composition analysis)

Pseudoscience (e.g., handwriting experts)

Difficulty in matching trace to a source especially when conclusions about rare events and unusual materials required

FORENSIC AND LEGAL PSYCHOLOGY

Mark Costanzo | Daniel Krauss | Fourth Edition

When Does a Trace “Match” a Source?

A match between a print left at a crime scene by a new, unworn shoe (like the prints in the top row) and a print left by a suspect’s new shoe would have little value in placing the suspect at the scene.

But a match with a print left by a well-worn shoe (like those in the bottom row) would be more useful in establishing that the suspect had been at the scene.

FORENSIC AND LEGAL PSYCHOLOGY

Mark Costanzo | Daniel Krauss | Fourth Edition

Modern forensic identification rests on comparisons between samples. The first sample usually includes trace evidence left at the scene of the crime (e.g., fingerprints, hair, skin cells, fibers from clothes) or trace evidence transported from the scene (e.g., carpet fibers, hair or blood from a victim)

Samples of the trace evidence are then compared to samples taken from a criminal suspect. If that comparison reveals that the features of the two samples are substantially similar and that there are no substantial, unexplainable differences, the comparison can be used to establish that the suspect was at the crime scene.

Basic Principles of Scientific Measurement: Reliability and Validity

Reliability: Consistency or repeatability of a measure or observation

Test–retest reliability (temporal consistency): High if a measure yields the same results over time

Interrater reliability (interobserver agreement): Degree to which two or more observers or analysts independently arrive at the same measurement

FORENSIC AND LEGAL PSYCHOLOGY

Mark Costanzo | Daniel Krauss | Fourth Edition

Measures must be reliable and valid.

Reliability

Reliability is the consistency or repeatability of a measurement or observation

Measurements shouldn’t fluctuate for no reason

FORENSIC AND LEGAL PSYCHOLOGY

Mark Costanzo | Daniel Krauss | Fourth Edition

Types of reliability -example

» Test-retest reliability means that if you take the same test twice, your score shouldn’t change dramatically over time

February

March

FORENSIC AND LEGAL PSYCHOLOGY

Mark Costanzo | Daniel Krauss | Fourth Edition

Types of reliability - example

» Interrater reliability means 2 or more analysts should independently arrive at the same conclusion

– Refers to consistency among judgments made by multiple trained, independent individuals

FORENSIC AND LEGAL PSYCHOLOGY

Mark Costanzo | Daniel Krauss | Fourth Edition

Basic Principles of Scientific Measurement: Reliability and Validity

Measurement validity: Technique measures what it is supposed to measure

FORENSIC AND LEGAL PSYCHOLOGY

Mark Costanzo | Daniel Krauss | Fourth Edition

Measures must be reliable and valid.

Reliability and Validity

» It is possible to have reliability without validity, but it is NOT possible to have validity without reliability!

– A test cannot be valid unless it is reliable because if a test does what it is supposed to, then it has to do it consistently to work

FORENSIC AND LEGAL PSYCHOLOGY

Mark Costanzo | Daniel Krauss | Fourth Edition

Scientific Foundations of Forensic Identification

DNA evidence history

1953: Watson and Crick published seminal (“A Structure for Deoxyribose Nucleic”)

Late 1984: Jeffreys and colleagues recognize forensic potential of DNA

1988: DNA introduced as evidence in U.S. courts (People v. Wesley)

CODIS maintained by FBI as largest, most frequently used DNA database in the world

FORENSIC AND LEGAL PSYCHOLOGY

Mark Costanzo | Daniel Krauss | Fourth Edition

“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.”

FORENSIC AND LEGAL PSYCHOLOGY

Mark Costanzo | Daniel Krauss | Fourth Edition

Scientific Foundations of Forensic Identification

DNA evidence

DNA is extracted and analyzed from biological evidence using computerized measuring instruments.

Genetic profiles are detected and displayed as alleles on a DNA strand and graphed.

When two profiles match, a random match probability (RMP) is calculated to estimate probability that match could occur by chance.

An imperfect DNA can yield a more subjective judgment of the analyst which raises the error risk; touch DNA challenges

RMPs are presented to judge or jury during trial.

FORENSIC AND LEGAL PSYCHOLOGY

Mark Costanzo | Daniel Krauss | Fourth Edition

Electropherogram

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Mark Costanzo | Daniel Krauss | Fourth Edition

A defendant’s DNA profile at three loci. The numbers in the boxes just below the peaks identify the specific alleles at each locus, and the lower boxes indicate the height of the peak for each allele.

Scientific Foundations of Forensic Identification

And so . . . DNA identification

Reliable and valid method

Most objective

Solid scientific foundation

Some limitations

FORENSIC AND LEGAL PSYCHOLOGY

Mark Costanzo | Daniel Krauss | Fourth Edition

Using Familial DNA Matches to Identify Criminal Suspects

The identification and capture of the Golden State Killer occurred by accessing familial DNA and matching it to crime scene evidence.

Searching public DNA databases does not require court approval.

What privacy concerns might such a search pose in future cases?

FORENSIC AND LEGAL PSYCHOLOGY

Mark Costanzo | Daniel Krauss | Fourth Edition

Scientific Foundations of Forensic Identification

Fingerprint history

1892: Galton introduces fingerprinting as method of identification (Finger Prints); individual abilities and psychological traits

Turn of century: Others developed detailed classifications for fingerprints

Today: Latent prints used in identification; process unlike and more involved than depicted in many television shows and movies

FORENSIC AND LEGAL PSYCHOLOGY

Mark Costanzo | Daniel Krauss | Fourth Edition

Galton: individual abilities and psychological traits can be objectively measured and the results quantified (assigned numerical values) to distinguish between people

Fingerprint Patterns

FORENSIC AND LEGAL PSYCHOLOGY

Mark Costanzo | Daniel Krauss | Fourth Edition

(a) In a loop pattern, the ridges enter from either side, recurve, and pass out or tend to pass out the same side they entered.

(b) In a whorl pattern, the ridges are usually circular.

(c) In an arch pattern, the ridges enter from one side, make a rise in the center, and exit generally on the opposite side.

Scientific Foundations of Forensic Identification

Fingerprint matching via ridge characteristics comparison

Bifurcations (single edge splits into two)

Ends (where ridge stops)

Crossovers (two ridges joined by bridge ridge)

Independence (short ridges with clear end points)

FORENSIC AND LEGAL PSYCHOLOGY

Mark Costanzo | Daniel Krauss | Fourth Edition

Ridge Characteristics. Characteristics such as bifurcations and ends are compared across different prints to assess whether the prints could have been made by the same person. (Equinox Graphics/Science Source)

Many examiners also take into account characteristics such as pores, ridge shape, ridge thickness, and the relative locations of all characteristics.

Scientific Foundations of Forensic Identification

Error source

Poor print quality

Examiner error exists

One dissimilarity doctrine ignored

Commonness or rarity of specific ridge characteristics not addressed

FORENSIC AND LEGAL PSYCHOLOGY

Mark Costanzo | Daniel Krauss | Fourth Edition

In the legal system, the critical issue is not whether every fingerprint is unique; rather, the critical issue is the probability of error—that is, the likelihood that a fingerprint will be wrongly identified as matching the defendant (false positive error) and the likelihood that a print will be wrongly excluded as coming from the defendant (false negative error).

Scientific Foundations of Forensic Identification

Psychological biases in fingerprint identification

Contextual bias

Confirmation bias

Despite conflicting research findings, most forensic examiners do not purport bias problem

Infallibility

Person immunity to cognitive biases

Bias suppression by willpower

FORENSIC AND LEGAL PSYCHOLOGY

Mark Costanzo | Daniel Krauss | Fourth Edition

Even professional fingerprint examiners do not appear to be immune to contextual bias (e.g., emotions, expectations, and motivations) to taint one’s judgments.

Contextual bias: Tendency for extraneous influences in the immediate environment

Scientific Foundations of Forensic Identification

And so . . . fingerprint Identification

Less objective than DNA analyses

Based more on judgment of examiner

Can be mores subjective

Cognitive biases

Contextual bias

Confirmation bias

Several limitations

FORENSIC AND LEGAL PSYCHOLOGY

Mark Costanzo | Daniel Krauss | Fourth Edition

Techniques of Weak or Unknown Validity

Bullet striation match: No widely accepted standards for number, size, or types; subjective analysis and intuitive standards may be employed

FORENSIC AND LEGAL PSYCHOLOGY

Mark Costanzo | Daniel Krauss | Fourth Edition

Magnified striation pattern on bullets, aligned to determine whether the bullets match. (John Nixon, Athena Research & Consulting)

Techniques of Weak or Unknown Validity

Tool match: No persuasive research validating tool mark analysis

Teeth match: Bowers found high false positive rate among results of practicing forensic dentists

FORENSIC AND LEGAL PSYCHOLOGY

Mark Costanzo | Daniel Krauss | Fourth Edition

Other Weak Techniques

» Handwriting Analysis

Size, slant, shape of letters

Error rates ranging from 40-97%

Problem:Variation over time; can’t prevent tampering

FORENSIC AND LEGAL PSYCHOLOGY

Mark Costanzo | Daniel Krauss | Fourth Edition

Reducing Error and Bias in Forensic Identification

Continued development and use of DNA identification

Introduction and passage of “changed science” laws

Examples

California Penal Code § 1473, 2017

Texas Code of Criminal Procedure, article 11.073

FORENSIC AND LEGAL PSYCHOLOGY

Mark Costanzo | Daniel Krauss | Fourth Edition

Reducing Error and Bias in Forensic Identification

» Ensuring proper handling of trace evidence

» Routine retesting of trace evidence – inter-rater

» Utilizing blind and double blind testing (for actual testing and to check accuracy of examiner)

» Designating evidence as property of legal system

» Require extensive experience and training in science for forensic examiners/scientists (plus judges, attorneys, and LE)

FORENSIC AND LEGAL PSYCHOLOGY

Mark Costanzo | Daniel Krauss | Fourth Edition

Communicating the Similarity of a Trace and a Source

Ways forensic identification experts communicate their findings (Thompson & Cole, 2007)

Qualitative statement: Involves subjective, nonstatistical statement of match strength

American Board of Forensic Odontology; six degrees of certainty

Simple match: Matches share characteristics

Match plus statistics: Includes statistics to determine how rare or common; places match in context

Individuation: Indicates detailed and perfect match

FORENSIC AND LEGAL PSYCHOLOGY

Mark Costanzo | Daniel Krauss | Fourth Edition

Six degrees of certainty about whether a suspect is the source of a bite mark: (1) inconclusive, (2) suspect is not the source, (3) improbable that the suspect is the source, (4) possible that the bite mark came from the suspect, (5) probable that the bite mark came from the suspect, and (6) source attribution to a reasonable medical certainty

Communicating the Similarity of a Trace and a Source

Strategies

Providing jurors with information about how often forensic scientists are wrong

False positive and false negative rates

Not allowing claims of professional experience to substitute for solid scientific foundation

Replacing word “match” with more objective terms

Consistent with; similar to

FORENSIC AND LEGAL PSYCHOLOGY

Mark Costanzo | Daniel Krauss | Fourth Edition

Jurors and Trace Evidence

» Can jurors assess RMP statistics?

Jurors have difficulty interpreting probability/statistical statements

› Defendant matches the perp on a characteristic found in only 4% of the population – what does this mean?

Distinctions in RMP statistics has little bearing on judgments of guilt

FORENSIC AND LEGAL PSYCHOLOGY

Mark Costanzo | Daniel Krauss | Fourth Edition

Hot Topic: Is There Really a “CSI Effect”?

TV dramas are unrealistic

Some prosecutors feel jurors may expect conclusive forensic evidence in every case; may lead to fewer convictions

Limited research findings suggest CSI effect does not occur

FORENSIC AND LEGAL PSYCHOLOGY

Mark Costanzo | Daniel Krauss | Fourth Edition

Reducing Error and Bias

Solid scientific foundation demonstrating the validity of an identification technique is a precondition for trustworthy analysis

Proficiency testing and certification of forensic analysts

Blind testing

Physical evidence viewed as legal system property

FORENSIC AND LEGAL PSYCHOLOGY

Mark Costanzo | Daniel Krauss | Fourth Edition

How Jurors Think About Trace Evidence

Juror considerations

Detailed technical information

Statistical statement about probabilities

Combine complex testimony and assign appropriate weight to identification evidence in verdict decision

Juror behaviors

Tend to place too little weight on probabilities

Have difficulty making sense of statistical statements

Are usually unaware of limited scientific foundation for fingerprint identification and unaware of weaknesses in matching processes

FORENSIC AND LEGAL PSYCHOLOGY

Mark Costanzo | Daniel Krauss | Fourth Edition

And so . . .

Even if technological fixes are found, fundamental problems remain

Weak scientific foundation for many forms of identification evidence

Risk of contamination or misinterpretation of the trace evidence

How the strength of a match or near match is communicated to jury or judge

FORENSIC AND LEGAL PSYCHOLOGY

Mark Costanzo | Daniel Krauss | Fourth Edition

Bottom Lines

» Two very important questions should underlie the admission of and reliance upon forensic evidence in criminal trials:

Is the forensic discipline founded on a reliable and valid scientific methodology?

Does this forensic discipline rely on human examination and interpretation of evidence?

Chapter 4

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