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Challenges in Explaining DNA Evidence to Jurors: A Defense Attorney’s Point of View. The Science of DNA Profiling: A National Expert Forum Dayton, OH August 14, 2005 Edward J. Ungvarsky, Special Counsel (202) 824-2301,

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Challenges in explaining dna evidence to jurors a defense attorney s point of view l.jpg

Challenges in Explaining DNA Evidence to Jurors: A Defense Attorney’s Point of View

The Science of DNA Profiling: A National Expert Forum

Dayton, OH August 14, 2005

Edward J. Ungvarsky, Special Counsel

(202) 824-2301,

Public Defender Service for the District of Columbia

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Introduction/Goals Attorney’s Point of View

  • What do we know about what jurors think of DNA evidence

  • Pretrial: Evaluating DNA evidence with jurors in mind

  • Trial: Presenting DNA evidence with jurors in mind

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What do we know about what Attorney’s Point of View

jurors think of DNA Evidence?

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“CSI Effect” Debate in Popular Media Attorney’s Point of View

  • Prosecutor’s complaints

    • Not getting convictions where used to

    • Being held to too high a standard

    • false, impossible forensics

    • Expensive and burdensome

  • Simon Cole analysis

    • TV shows may make jurors more inclined to convict because they falsely portray forensic evidence as unambiguous and certain

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Juror Questionnaires/Experiments Attorney’s Point of View

  • PDS – December 2003

    • DNA is most reliable form of evidence

  • NIJ Study – Hon. Michael Dann

    • Less than 1/3 successfully rejected P’s fallacy

    • contamination

  • Jonathan Koehler articles

    • Difference between approaches

      • Odds v. probabilities

      • Jurors better understand odds

  • Anecdotal

    • Interviews with jurors from high profile cases

    • DC jurors

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Summary of Conclusions Attorney’s Point of View

  • Jurors don’t understand forensic DNA profiling

  • Jurors see DNA as most reliable forensic science

  • Jurors CAN be persuaded that DNA is not infallible (n.b.: necessity for double negative)

  • Different statistical approaches have demonstrably different effects

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General Myths that Need Debunking Attorney’s Point of View

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Pretrial Preparation Perspectives in Mind

  • Need to know the DNA evidence as well as the experts

  • Once you understand what DNA evidence is and isn’t, you should immediately begin to evaluate its impact on your choice of, and development of, your defense theory

  • You need to think about ways to explain the presence of DNA in a way that jurors will understand and accept

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Understanding DNA Evidence Perspectives in Mind

  • Meetings

    • National meetings

      • Promega, AAFS, Forensic Bioinformatics

      • Local trainings

  • Experts

    • At this meeting

    • Others

    • Develop own

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Understanding DNA Evidence Perspectives in Mind

  • Web:


    • Jennifer N. Mellon, Note, Manufacturing Convictions: Why Defendants Are Entitled to the Data Underlying Forensic DNA Kits,51 Duke L.J. 1097 (2001), available for free online at

  • Scientific Literature

    • Journal of Forensic Sciences

    • Forensic Science International

    • Non-Forensic Journals (Nature, Genetics, etc.)

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NRC I and NRC II Perspectives in Mind

  • Nat’l Research Council, DNA Technology in Forensic Science (1992) [“NRC I”]: There is lots of good language and it is easy to read.

  • Nat’l Research Council, The Evaluation of Forensic DNA Evidence (1996) [“NRC II”]: For many, it is the “bible” of forensic DNA. You should own a copy or have access to one.

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John Butler Perspectives in Mind

John M. Butler, Forensic DNA Typing: Biology, Technology, and Genetics of STR Markers (2d ed. 2005)

Dr. Butler is a scientist at NIST. His treatise is THE forensic DNA book to own and to present before a forensic scientist in court. The second edition is over 600 pages.

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Forensic DNA Treatises Perspectives in Mind

  • Forensic DNA Evidence Interpretation (John Buckleton, Christopher M. Triggs & Simon J. Walsh eds., 2005). Scientists from outside the United States often bring a different perspective from conventional wisdom in the U.S., where the FBI and government crime laboratories are so dominant.  

  • Norah Rudin & Keith Inman, An Introduction to Forensic DNA Analysis (2d ed. 2002). A standard textbook in forensic science programs across the country.

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Treatises: Forensic DNA Statistics Perspectives in Mind

  • David J. Balding, Weight-of-Evidence for Forensic DNA Profiles (2005). Dr. Balding is a professor of statistical genetics at Imperial College in London, England, who, among other things, has co-authored some of the leading articles on the interpretation of cold hit DNA evidence.   

  • Ian W. Evett & Bruce S. Weir, Interpreting DNA Evidence: Statistical Genetics for Forensic Scientists (1998). With good examples to help you through the math.

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Treatises: Statistics Perspectives in Mind

  • David Freedman et al., Statistics (3d ed. 1998): This is a university textbook, with intuitive examples, written with a minimum of difficult mathematics.

  • Michael O. Finkelstein & Bruce Levin, Statistics for Lawyers (2d ed. 2001): Like Freedman, but more targeted.

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Discovery Perspectives in Mind

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Obtain Discovery Perspectives in Mind

Why you need the raw data:

  • Analyst may have miscalled alleles

  • To see the graphs of reagent blanks & control samples to look for contamination

  • Allows your expert to reanalyze data or show data at different settings

  • To show the jury at trial

  • To check for manipulation of data by analyst

  • Get bench notes of analyst as well

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Review Discovery Perspectives in Mind

  • Signs of contamination in reagent blanks and positive and negative controls

  • Masked contributors (misinterpretation of mixtures)

  • Miscalled alleles (highly subjective “art”)

    • “Artifacts”

    • “Stutter”

    • “Allelic dropout,” false peaks

    • MAC v. P

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Consult with Independent Expert Perspectives in Mind

  • Another set of eyes

  • Expertise and experience

  • Not replacement for own assessment of DNA evidence

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Put Yourself in Jurors’ Shoes Perspectives in Mind

  • How is the DNA evidence significant to the charges?

  • How does it relate to the remainder of the evidence?

  • What is an innocent explanation for the DNA evidence?

    • MUST have jurors think about DNA from the perspective of the defense

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Evaluating DNA Evidence at Trial From Defense Perspective Perspectives in Mind

  • Your client is the source of the DNA

    • Was involved in the offense but was legally justified: consent, self-defense

    • Was not involved in the offense: DNA transfer, prior contact, malfeasance, contamination

  • Your client is not the source of the DNA

    • Coincidental match

    • False reported “match” or inclusion (failure to properly call alleles, etc.)

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Transfer Perspectives in Mind

  • Transfer: through towels, laundry basket, brushing against someone on the subway

  • Other reasons for client’s saliva, skin cells, blood, semen, hair to be at scene (e.g., frequent visitor at decedent’s home)

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Malfeasance Perspectives in Mind

Deliberate contamination with client’s profile in testing process

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Contamination Perspectives in Mind

  • Can occur at collection, extraction, amplification, injection

  • Look at raw data for reagent blanks and positive and negative controls

  • Degraded or low copy # DNA increases risk

  • Look to see if laboratory’s protocols were followed

  • Look at sufficiency of protocols, proficiency tests, and reviewing process

  • Have a theory for why client’s DNA would be near sample during collection or testing

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Contamination Perspectives in Mind

Contaminated Positive Control

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Inaccurate Calling of Data Perspectives in Mind

Masked contributors (misinterpretation of mixtures)

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Inaccurate Calling of Data Perspectives in Mind

Miscalled alleles (interpretation, not science): stutter

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False Positives: Josiah Sutton Perspectives in Mind

  • Complainant ID’d Sutton as rapist; Sutton convicted and sentenced to 25 years

  • Rain from holes in roof of lab may have caused contamination

  • Recent retesting exonerated Sutton

Alleles found: 1.1, 2, 4, 4.1

One rapist: (2, 4)

Other rapist must be: (1.1, 4.1)

Sutton: (1.1, 2)

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Coincidental Matches Perspectives in Mind

  • There is a match, but it is coincidental

  • Perpetrator could be a relative (still difficult)

  • Perpetrator could be a non-relative (should concentrate on lowering the RMP through statistical arguments)

  • 6/16/89 U.S. Open – 4 pro golfers made a hole in one on the same hole, same day. P = 1 in 89 quadrillion (Harvard professor to Boston Globe)

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Independent Testing Perspectives in Mind

  • Different expert than consulting expert who reviews prosecution’s work

  • Results of independent testing

    • Whether to conduct independent testing is complicated judgment call

    • Face possibility that exclusion may not occur

    • Assume jury will find out you tested

      • Lab discloses

      • Prosecution witness or attorney blurts out

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During Preparation, Remember the Jurors Perspectives in Mind

  • Software printouts – what would juror think about this?

  • Interviewing prosecution experts – what questions would a juror ask this person?

  • Interviewing independent experts

    • May sound great but is it understandable

    • Expert both good on merits and personable

  • Quality Control – what has lab done to stop recent problems from occurring in its lab

  • Ability to Test – what could prosecution have tested but didn’t?

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Presentation of the DNA Evidence at Trial Perspectives in Mind

with Jurors’ Perspectives in Mind

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DNA Trial Counsel? Perspectives in Mind

  • Different viewpoints

    • My viewpoint: You don’t have eyewitness counsel or informant counsel, so you don’t need DNA counsel. You don’t have DNA jurors, don’t have DNA counsel.

    • If DNA Counsel – Counsel should be present entire trial

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Presentation of DNA: Voir Dire Perspectives in Mind

  • Jury Selection

    • What do jurors think about DNA evidence

    • What do jurors think about OJ Simpson case

    • Learn about your jurors

    • Educate your jurors

    • Open-ended questions

    • Questionnaires

    • Get commitment from jurors that they will not convict unless they UNDERSTAND the DNA evidence

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Presentation of DNA: Opening Statement Perspectives in Mind

  • Put forward your understanding of the DNA

  • Incorporate DNA evidence with rest of anticipated evidence

  • Don’t give away secrets

  • Don’t talk about what you don’t understand

  • Don’t bore the jury

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Cross-Examination Perspectives in Mind

  • “Bias is Always Relevant”

    • Don’t put witness on pedestal, treat like any other witness

    • “Who is your client?”

  • Determine what the LIMITED scope of C-X should be based on your defense theory and what you are planning to question

    • i.e., don’t question credentials of prosecution witness who will admit to DNA transfer

  • Question the SCOPE of expert’s expertise

    • Forensic scientist v. statistician

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Practice Pointers Perspectives in Mind

  • Short, targeted cross-examination

    • One fact per question, building upon each other, lead

    • Use the jargon correctly – Don’t Use Jargon

    • Keep it to 30-45 minutes (2 days = 2 hour jury deliberation, conviction)

    • Preempt fallacies

      • “Now doctor, saying that RMP is 1 in 100 does NOT mean that there is 1 in 100 chance that the suspect is not the source of the DNA, right?

      • “And that false assumption is referred to in the literature as the prosecutor’s fallacy, right

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Prosecution DNA Expert Perspectives in Mind

Do not spar!

Don’t try to out-expert the expert; you’re an intelligent, well-informed layperson, not scientist, and jurors know that

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Evidence of 3 Perspectives in Mindrd Party

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Evidence of 3 Perspectives in Mindrd Party

~ 12 %

  • FBI protocols: % > 12 = genetic profile

  • FBI analyst: “technical artifact”

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Do You Call Your Own Expert? Perspectives in Mind

  • Differing opinion/interpretation of DNA results

  • Prosecution bears burden of proof

  • Set Up battle of the experts

    • What will your expert say?

    • You must understand DNA and talk about testimony with expert before expert testifies

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Direct Examination Perspectives in Mind

  • Direct Examination should be about aslong as attention span between breaks (1.25 – 1.5 hours)

    • Includes qualifications

  • Use analogies and visuals

    • TV, not radio, generation

    • Cinderella analogy

  • Explain through questioning difference between your expert’s area of expertise and prosecution’s, and why that matters

  • Prepare expert for cross-examination

  • Prepare re-direct examination – LAST WORD!

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Closing Argument Perspectives in Mind

  • Visuals? Yes, yes, yes.

  • PowerPoint? No, no, no.

    • Breaks down

    • Inflexible

    • Focus should be on the lawyer and the connection you have made with jury over course of case

  • Simple – Do not get overly technical

  • Demystify; bottom line, science v. art

  • Empower jurors

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Questions? Perspectives in Mind

  • Edward J. Ungvarsky(202) 824-2301

  • PowerPoint and Case materials