Cross Examining Expert Witnesses: Unique Tactics

Christine Funk

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— Updated on June 23, 2020

Cross Examining Expert Witnesses: Unique Tactics

Cross examining expert witnesses can be daunting. After all, you are challenging someone who has made their career understanding the topic. You should spend a considerable amount of time preparing cross examination questions with your own expert’s help before attempting to challenge the others side’s expert. If you’ve selected a winning expert witness, then they should be well versed in, and routinely apply, the principles of their specific discipline. They are your best resource for gaining a solid understanding of the discipline, which can help you in court if by chance the other side’s expert witness “goes off script.”

Common Topics for Cross Examination

The common topics for cross examination include:

·  Background of the expert
·  Training of the expert
·  Experience of the expert
·  Improper collection of the evidence
·  Incomplete collection of the evidence
·  Improper analysis
·  Failed controls or lack of controls
·  Insufficient data to draw a conclusion
·  Too much data, which leads to examiner bias
·  Other forms of examiner bias
·  Improper conclusions
·  Bad science
·  Rogue scientists in the same lab
·  Rogue scientists in the same discipline
·  Laboratory or discipline failures

This is not an exhaustive list, however, this should give you a starting place.

Before Wandering into the Realm of “Unique Tactics”

Of course, your first task, as a lawyer, is to become familiar with, and proficient in, the rules of court, including, how to properly phrase a cross examination question, how to handle a witness who is being difficult, and how to introduce, and lay the foundation for, an exhibit. Your next task, as a lawyer working on a case that requires expert witnesses, is to learn the science, both generally, and specifically how the science relates to the case at hand.

If you find yourself in trial, one can only presume either a) you are trying a case with no offer and therefore no incentive to resolve it pretrial; or b) you are trying a case because you have battling expert witnesses, who have different stances on the evidence at hand; or c) the expert testimony is not dispositive to the resolution of the case. Whether you are challenging the evidence, the conclusions, the science, or the scientist, or whether you are simply seeking to use the evidence or the expert’s conclusions to highlight an important part of your case, there are approaches you can take, once you are certain you have mastered trial fundamentals, which can assist the trier of fact see the evidence in your favor.

These tactics can also be used during depositions or during pretrial meetings. Lawyers should carefully consider the benefits of using tactics pretrial against the loss of the element of surprise, and whether the element of surprise is helpful to your case. Depositions can also be an opportunity to “practice” the method.

The Importance of Using Visual Aids

Visual aids provide supplementary benefits the trier of fact, namely:

·  Assist in understanding
·  Assist in remembering important facts
·  Increase the jurors’ interest
·  Provide visual guidance
·  Support learning

No matter how brilliant your closing argument is, you can’t get back into the jury room to repeat it. Exhibits, on the other hand, will go back to the jury room and a well-made exhibit offers ongoing silent testimony for the trier of fact long after the witness gets off the stand.

Using Visual Aids During Cross Examination

Using visual aids during cross examination of the other side’s expert is risky business. But the payoff can be exponentially higher than using visual aids with your own expert. Of course, attorneys should carefully script their cross examination, relying on known facts and supportable premises. You should have relevant texts, studies, and data close at hand, lest the expert become resistant.

Using the Expert’s Work as an Exhibit

In the right case, the expert’s own work can be used as an exhibit helpful to the jury. Consider, for example, a case involving forensic DNA evidence. The forensic biologist testing the evidence has answered the questions put to her, “Does the DNA on the sweatshirt match the defendant?” and “Does the DNA on the hat match the defendant?” The scientist provides the answer to both of these questions, “No.” As such, the government takes the position the sweatshirt and the hat found at the scene are irrelevant.

Imagine, however, your theory of the case is that the crime was committed by an as yet unidentified perpetrator. Imagine further you have carefully reviewed the data with your expert, and you believe there is a profile on the sweatshirt that matches the profile found on the hat. How to convey that presence of an identified profile on two pieces of evidence that you find relevant and consistent with your third-party perpetrator theory?

Avoid overwhelming the jury by breaking down the data into bite-sized pieces. Blow up each locus on the electropherogram or the scientist’s profile table, either in a PowerPoint (be sure to provide each juror a copy for reference during the cross) or on good old-fashioned foam board. Use the exhibit while you ask the expert your questions, like this:

“Looking at sample 19A, the sweatshirt, is there a profile at D3 of 14, 16?”

“And looking at sample 22, the hat, is there also a profile of 14, 16 at D3?”

“Could the person who left the DNA on the sweatshirt also have left their DNA on the hat?”

“Moving on to Tho1. Looking at sample 19A. . .” you get the idea.

Using the Expert’s Work to Create a New Exhibit

Sometimes, the best exhibit is one you create yourself. Imagine you find a mathematical error in the expert’s work. First, think long and hard about whether tactically it is better to question this at a deposition or pretrial, as opposed to springing this on an expert on the stand. Typically, if the error is in and of itself harmless, but can be used to call into question the analyst’s approach, you may want to save it for trial, minimizing the other side’s opportunity for damage control.

Most experts will not engage in performing mathematical analysis on the stand. There are a number of very good reasons for this, associated with the risk of error, the lack of a second reader, and accreditation standards. None the less, you can do your own math, and ask the expert if they agree, like so.

“I notice you calculated your result by adding three figures.”

“800?” *Writes 800 on a large piece of paper*

“400?” *Writes 400 on a large piece of paper in a column under 800*

“And 253?” *Writes 253 on a large piece of paper in a column under 400*

“I ask you to direct your attention to the calculator displayed on the screen. Would you agree with me I have entered ‘800’ into the calculator?”

“Would you agree I am now adding 400?”

“Would you agree I am now adding 253?”

“Would you agree the calculator reflects a sum total of 1453?”

“Yet your report indicates a sum of 14,530?”

Obviously, this is a simple mathematical error, but it illustrates the point.

A Final Word of Caution

Using exhibits with opposing experts can be a unique approach to cross examination that illustrates relevant points. However, attorneys are encouraged to practice this approach repeatedly with a colleague or friend, with an eye towards ways this could go horribly wrong. Anticipating problems allows one to address them in advance.

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