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 • Cross Examination Issues • Redirect • Outside Experts/Rebuttal Witnesses
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 • 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 • 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 • 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 EXAMINATION • What items of evidence did you examine? • What did you find? • What is the significance of the match?
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” 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 Trial Depending on number of items tested, direct testimony of DNA evidence can be completed in 30 minutes to 1 hour
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 Topics • Population databases/ethnic background of defendant • “It was the brother/father/uncle/etc.” • Reliability of the technology - quality control issues
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 • 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 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 • Scientific validation • Peer review • Reliability • General acceptance in relevant scientific community Judge determines degree of emphasis for each condition.
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 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 • Publications in appropriate scientific journals. • Presentations at scientific meetings/conventions.
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.
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 • 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 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.
NRC I First Report Issued by National Academy of Sciences in 1992 • Methods Reliable • 3-4 probe match rare • Use product rule • Ceiling “principle”
NRC II Second report issued in May of 1996 • Report actual frequency • Recommended re-test • Suggested “identity” • The “Bible”
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!
New individual formed during conception: ½ of DNA from mother, ½ from father
Review of DNA Structure CHROMOSOME
Complementary Base Pairs A T = Adenine Thymine T A Guanine = Cytosine G C C G
HUMAN IDENTITY TESTING IS BASED ON POLYMORPHISMS POLYMORPHISM = “MANY FORMS” DIFFERENCES BETWEEN/AMONG INDIVIDUALS
Examples of Human Polymorphisms • Hair color • Eye color • Height • Blood type (ABO, Rh, etc.) • Tissue type (HLA)
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 • MOST COMMONLY OCCURRING ARE VARIABLE NUMBER OF TANDEM REPEAT “VNTR” TYPE
Polymerase Chain Reaction • Molecular Xeroxing of targeted areas of DNA determined to contain information. • Used in • research • diagnostics • forensics
Three PCR cycles yields eight-fold amplification, or 23 copies of original.
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
PCR-based Low-quantity DNA Amenable to automation Degraded DNA Rapid typing STRs Highly discriminating Discrete alleles Abundant in genome Non-isotopic ShortTandemRepeats
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
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