Expert Testimony Guidelines for Lawyers and Judges
Dive into a comprehensive program focusing on DNA testing, pre-trial preparation, cross-examination, and expert testimony in legal proceedings. Explore the nuances of DNA limitations, problematic questions, and the intricacies of fingernail and ligature testimony. Gain insights on effective communication, language clarity, and the expert's duty for accurate testimony.
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Presentation Transcript
Testimony Session DNA PROGRAM FOR LAWYERS AND JUDGES NOVEMBER 2-3, 2023
Pre-Trial Preparation MEET WITH YOUR EXPERT ASK EVERY QUESTION / USE OF SCRIPTS AGREE ON A VOCABULARY UNDERSTAND WHAT IS IN YOUR FILE UNDERSTAND THE LIMITATIONS
Pre-Trial Preparation Areas for cross examination Exhibits & demonstratives Understanding the expert s testimony style Share information
Sticking to what was agreed upon during pre-trial Testimony Guiding Principles Clear, jargon-free, and concise language The expert's duty to correct during testimony, during trial, after trial decision rendered
DNA testing is not error- free Limitations of DNA Testing DNA testing helps address who The DNA testing/interpretations cannot help address how or when
Some examples of problematic questions are: A hypothetical transfer scenario is posed is it (more) likely? Is (this) possible or not? Could (this) explain the DNA results? DNA "Transfer" preview Impact of licensure and professional code of responsibility obligations Texas Rules of Evidence 702, 705
Fingernail Testimony Q: It says: Due to the quantity and/or quality of DNA obtained, no conclusions can be made regarding the DNA profile obtained from the additional contributor(s). What does that mean? A: It means that with a mixture we re dealing with a lot more information. And when I sit down and look at the mixture and compare it to Sebastian Bruno, I was not able to make a clear determination if he was a contributing individual to that mixture. I could not make a conclusion. Q: So, in that circumstance, you could not exclude him from being a possible contributor to that DNA? A: Correct. Takeaway and Discussion The danger of asking these questions with the goal of simplicity it puts the expert in a bind for an accurate response What certain words mean in different contexts (inconclusive, uninterpretable)
Ligature Testimony Q: I m sure you have seen some pretty large numbers in your testing before, and earlier on direct I think you said 1 in 4 quadrillion for the vaginal swabs. That s a pretty big number--I don t remember how many zeros you said that is. But when you look at the statistic for the ligature, 1 in 835, that s a much smaller number there aren t any zeros. That s not very strong, wouldn t you agree? A: I would agree, it isn t a very strong statistic. Takeaway and Discussion Regardless of the value, do not conflate the statistic with the overall strength of the case. It is one part of the overall case to be considered with the other evidence. The CPI is used to estimate the proportion of unrelated individuals in the population that could be included as possible contributors to the profile. The CPI statistic is not related to chances of innocence/guilt.
Since the DNA on the ligature matches Sebastian, there is a one in 835 chance that he is innocent. Misusing stats during closing arguments The population of the Austin metro area is nearly 2.5 million people. If one out of every 835 people could have left this DNA, then there are 2,994 other people who could have committed this crime. The DNA results on the ligature represent 835 reasons to convict the defendant.
Vaginal Swab Testimony Q: You indicated that in your opinion the fact that you saw three intact sperm on the slides indicated that the sexual activity had to have been quite recent? A: Yes. Q: Based on your knowledge, training, and experience how long a time frame are we talking about that you would expect a sperm to be able to stay intact. A: I have published documentation that says 26 hours is the outside length of time that tails will remain on a sperm head inside the vaginal tract of a female. Takeaway and Discussion Challenges with conclusions about source of DNA (semen) as well as persistence of intact sperm and how the expectations of the expert can/should be conveyed to the court What is the best way to convey these opinions?
DNA "Transfer" Issue Spotting CAUTION FLAG: How do we all feel about testifying to opinions that are not underpinned by our notes and reports? Vaginal swab results Does the potential timing of the deposition of the DNA have an impact on your case? Biological material characterization (sperm, blood, etc) Persistence of DNA (sperm intact versus not, quantity) Expectations about the DNA profile results if from close to crime versus 2 days prior Sweatshirt cuttings results Does when or how the DNA arrived on the item have an impact? Biological screening characterization (only ALS) How long have the stains been there? Do these results matter (to the questions in the case)?
ISSUE SPOTTING EXPERT STATEMENTS It's possible that the semen found on the sweatshirt was transferred from a previous consensual sexual encounter. It is also possible that the semen was ejaculated directly onto the sweatshirt. Observing these DNA results is 100 times more likely if the DNA was ejaculated directly onto the sweatshirt than if it was transferred by some other way. It is 100 times more likely that the semen found on the sweatshirt is from direct contact rather than indirect contact. Research has demonstrated that DNA can be transferred in detectable quantities by various intermediate ways.
ISSUE SPOTTING EXPERT STATEMENTS It's possible that the semen found on the sweatshirt was transferred from a previous consensual sexual encounter. It is also possible that the semen was ejaculated directly onto the sweatshirt. Observing these DNA results is 100 times more likely if the DNA was ejaculated directly onto the sweatshirt than if it was transferred by some other vector. It is 100 times more likely that the semen found on the sweatshirt is from direct contact rather than indirect contact. Research has demonstrated that DNA can be transferred in detectable quantities by various intermediate vectors. understand what the DNA results mean if the questions are about how or when. Opinions vary on the validity of "it's possible" statements because the statements in themselves do not require an expert opinion (anything is possible). There is no data to support if this approach is helpful - or not - to factfinders. (Is this the lane of the scientist?) Though this statement is correct in that the opinion is about the results (not about what happened) - there is not expert or legal agreement regarding the validity of this statement. Nothing about this statement is acceptable. It is a direct opinion regarding how the DNA arrived on an item. We can never know this answer. Though this statement is correct the argument could be posed about how whether it is helping (anyone)
