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Appendix 19. DNA. THE PRESENTATION OF DNA EVIDENCE IN COURT. Alan Giusti DNA Analysis Unit I FBI Laboratory, Washington, D.C. The Presentation of DNA Evidence. Admissibility Hearings Direct Examination Cross Examination Issues Outside Experts Trial Presentation Direct Examination

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the presentation of dna evidence in court
THE PRESENTATION OF DNA EVIDENCE IN COURT

Alan Giusti

DNA Analysis Unit I

FBI Laboratory, Washington, D.C.

the presentation of dna evidence
The Presentation of DNA Evidence
  • Admissibility Hearings
    • Direct Examination
    • Cross Examination Issues
    • Outside Experts
  • Trial Presentation
    • Direct Examination
    • Cross Examination Issues
    • Redirect
    • Outside Experts/Rebuttal Witnesses
presentation of evidence
Presentation of Evidence

BE PREPARED!

  • Extensive documentation of analyses conducted.
  • Strict adherence to protocols
    • Trials can be one to two years after lab work completed; thorough notes and adherence to the protocol greatly reduces expert witness’s uncertainty during testimony
  • Pre-trial consultations and meetings critical!
types of evidence
Types of Evidence
  • Cigarette butts, stamps, envelopes
  • chewing gum, threads
  • baseball caps, ski masks, headbands
  • Small blood spatter, fingernail clippings
  • fecal material, vomit
  • toothbrushes, hair brushes, eyeglasses
  • phone receivers, pens, false teeth
presentation of evidence at trial
Presentation of Evidence at Trial
  • KISS (Keep it simple, stupid)
  • Brief description of DNA testing process (15-20 minutes)
  • Introduction of evidence and findings of serological examinations (if applicable)
  • Results of DNA examinations
  • Conclusions drawn from DNA tests
  • Significance of a DNA match
direct examination
DIRECT EXAMINATION
  • What is DNA?
  • Can DNA be used to distinguish individuals?
  • How is this done?
  • What are the possible outcomes of a DNA comparison?
  • What is the significance of a DNA “match?”
direct examination1
DIRECT EXAMINATION
  • What items of evidence did you examine?
  • What did you find?
  • What is the significance of the match?
source attribution the identity calculation
Source Attribution(The “Identity” Calculation)
  • This calculation is used to determine if a DNA profile is so rare that it becomes unreasonable to suppose that a second person in the population might have the same profile.
source attribution the identity calculation1
Source Attribution(The “Identity” Calculation)
  • The conclusion drawn by the analyst is that an individual is the source of the DNA obtained from a forensic unknown, to a reasonable degree of scientific certainty.
  • It does not mean that the DNA profile is unique to the exclusion of all others.
presentation of evidence at trial1
Presentation of Evidence at Trial

Depending on number of items tested, direct testimony of DNA evidence can be completed in 30 minutes to 1 hour

cross examination topics
Cross Examination Topics
  • Contamination at crime scene / during evidence collection
  • Contamination by laboratory
  • Error rates
  • When DNA was deposited
  • Consent (sexual assault cases)
cross examination topics1
Cross Examination Topics
  • Population databases/ethnic background of defendant
  • “It was the brother/father/uncle/etc.”
  • Reliability of the technology - quality control issues
redirect
Redirect
  • Recognize topics where testimony of DNA analyst may be limited by opposing counsel (“Just answer yes or no, please”)
  • Attack hypothetical arguments
  • If applicable, emphasize possibility of re-testing specimens, or testing of other relatives
outside experts
Outside Experts
  • Scientists in the fields of molecular biology and population genetics will generally support technology and findings
  • Can be used also to contradict outside experts of opposing counsel
  • Pre-trial preparation - small group of defense experts with standard approaches - easily rebutted
admissibility of new technologies
Admissibility of New Technologies

Daubert v. Merrell Dow Pharmaceuticals (1993)

  • Federal standard for acceptance of new technologies.
  • Trial judge acts as “gatekeeper” - determines admissibility of scientific evidence/expert testimony.
daubert conditions
Daubert Conditions
  • Scientific validation
  • Peer review
  • Reliability
  • General acceptance in relevant scientific community

Judge determines degree of emphasis for each condition.

scientific validation
Scientific Validation
  • Extensive research in the development of a new technology.
  • Once process developed, reliability of technology determined by repetitive experiments - same results from a sample every time.
scientific validation1
Scientific Validation
  • For forensic applications, technology applied to types of materials collected from crime scenes.
    • Simulated samples: Laboratory prepared samples subjected to chemical and environmental insults.
    • Actual case specimens from adjudicated cases.
peer review
Peer Review
  • Publications in appropriate scientific journals.
  • Presentations at scientific meetings/conventions.
reliability
Reliability
  • Error rate: in the performance of the test, what percentage of the time will the test give an incorrect answer?
    • False inclusion most serious error in forensic human DNA analysis.
    • Failure to identify a virulent pathogen (false exclusion) equally dire.
reliability1
Reliability
  • Reliability of test should be determined during development and validation phase.
  • Current human DNA analysis protocols designed to avoid errors - numerous check points during procedures.
  • Errors can occur during test, but there is no fixed error rate.
general acceptance
General Acceptance
  • Adoption of technology by relevant scientific community.
  • Application of technology in other areas/fields - overarching acceptance of technology.
    • Ex.: PCR process used in many areas (medical, academic, forensic, etc.)
    • Specific application, e.g., forensic DNA analysis, may be debated.
admissibility
Admissibility

Be prepared to support technology with extensive documentation:

  • Detailed protocols
  • R&D and validation studies
  • Relevant publication references
    • Work of your own lab and other labs that have conducted research in the field.
slide25

NRC I

First Report Issued by

National Academy of

Sciences in 1992

  • Methods Reliable
  • 3-4 probe match rare
  • Use product rule
  • Ceiling “principle”
slide26

NRC II

Second report issued in

May of 1996

  • Report actual frequency
  • Recommended re-test
  • Suggested “identity”
  • The “Bible”
what is dna
WHAT IS DNA???
  • Deoxyribonucleic Acid
  • Genetic Blue print
  • Unique to you unless you have an identical twin
  • Robust molecule that can be obtained from evidentiary stains and tissues
  • 99.9% of DNA is IDENTICAL in all people!
slide31

Complementary Base Pairs

A

T

= Adenine

Thymine

T

A

Guanine

= Cytosine

G

C

C

G

human identity testing is based on polymorphisms
HUMAN IDENTITY TESTING IS BASED ON POLYMORPHISMS

POLYMORPHISM = “MANY FORMS”

DIFFERENCES BETWEEN/AMONG INDIVIDUALS

examples of human polymorphisms
Examples of Human Polymorphisms
  • Hair color
  • Eye color
  • Height
  • Blood type (ABO, Rh, etc.)
  • Tissue type (HLA)
types of dna polymorphisms
TYPES OF DNA POLYMORPHISMS

Length Polymorphism

  • The cat ranveryfast.
  • The cat ranvery,veryfast.

Sequence Polymorphism

  • Thecatis in the hat.
  • Theratis in the hat.
length polymorphisms
Length Polymorphisms
  • MOST COMMONLY OCCURRING ARE VARIABLE NUMBER OF TANDEM REPEAT “VNTR” TYPE
polymerase chain reaction
Polymerase Chain Reaction
  • Molecular Xeroxing of targeted areas of DNA determined to contain information.
  • Used in
    • research
    • diagnostics
    • forensics
pcr typing
PCR Typing
  • Typing based on sequence differences (dots)
    • DQ alpha typing
    • Polymarker
    • Interpretation Difficulties
  • Typing based on length differences (bands)
    • VNTR’s (D1S80, amelogenin)
    • STR’s
s hort t andem r epeats

PCR-based

Low-quantity DNA

Amenable to

automation

Degraded DNA

Rapid typing

STRs

Highly

discriminating

Discrete

alleles

Abundant in

genome

Non-isotopic

ShortTandemRepeats
slide41

ShortTandemRepeats

  • Arrays of short repeats (2-7 bp) that are repeated several times in tandem
  • >30,000 in the human genome
  • One every 10 kb
slide43

Flanking region of unique sequence

Allele:

AATG

AATG

AATG

AATG

AATG

5

AATG

AATG

AATG

AATG

AATG

AATG

6

AATG

AATG

AATG

AATG

AATG

AATG

AATG

7