STOP THAT EXPERT! How To Challenge Expert Witnesses

Posted by Michael E. Lyons | Nov 13, 2019 | 0 Comments

For those of you who have seen My Cousin Vinny, you may remember the epic scene when Vinny calls his fiancé, Mona Lisa Vito, to the stand as an expert in general automotive knowledge.

During a high-stakes criminal trial, Vinny defends his cousin and the cousin's friend, who have been accused of a murder they did not commit. In the case, the main piece of evidence is the tire mark left by the car that the real murderers used to flee the scene. Vinny tries to prove that those marks are not from his cousin's car, and therefore, his cousin and the friend are not the ones who committed the murder.

In order to prove that the marks did not belong to his cousin, Vinny calls Miss Vito to the stand as an expert in “all things cars.” The prosecution asks to “voir dire the witness” and proceeds to ask her a rapid-fire series of questions about cars. Miss Vito, having worked in her father's garage since childhood, clearly knows what she's talking about, and the prosecution is unable to discredit her. Therefore, she is qualified as an expert, giving her the ability to give an opinion on the tire marks—an opinion that ultimately decides the case.

While this was heavily dramatized for the big screen, this sort of thing actually happens in criminal cases. One side puts on an expert and the other attempts to discredit that expert through cross examination. Alternatively, one side can even call for a hearing pre-trial to stop the testimony altogether.

How do you challenge an expert witness?

In our previous blog, “When Do You Need An Expert Witness?,” we explained what an expert witness is and when having an expert witness may be useful or necessary for your case. Here, we are talking about how to challenge the admissibility of an expert witness testimony.

As we mentioned before, an expert witness is someone with special knowledge hired to provide their opinion for some purpose of the litigation. In order for that opinion to be used during the trial, the judge must determine whether the expert's testimony is admissible in the trial. Determining the admissibility of the testimony in a federal court usually occurs in a Daubert hearing. Here, we are focusing on challenging expert witnesses in federal court. State courts may have their own laws and standards about challenging expert witnesses.

Daubert Factors

In a Daubert hearing, the judge will determine whether the expert testimony is scientifically valid and can be applied to facts of the particular case, so as to make the testimony admissible. There are various factors that a judge will consider in determining the admissibility of the testimony. In accordance with Daubert v. Merrell Dow Pharms., Inc., (509 U.S. 579, 593-94 [1993]), those factors are:

  1. Whether the expert's theory and/or technique can be and has been tested
  2. “Whether the theory or technique has been subjected to peer review and publication”
  3. The potential error rate of the technique
  4. “The existence and maintenance of standards controlling the technique's operation”
  5. Whether the theory and/or technique has been generally accepted

So how do all those factors play out in a case?

In the My Cousin Vinny scenario described above, the prosecution should have focused on these factors to stop Miss Vito's testimony from being admitted. They could have questioned how Miss Vito came to the conclusion that the tire marks did not belong to Vinny's cousin's car. Maybe they could argue that it is not enough to look at the marks through a picture, but that she would have had to see them in person. Furthermore, they could argue that other car experts would have also had to see the marks in person, rather than relying on a picture. Lastly, the prosecution could try and argue that the error rate for determining what car makes certain tire marks based on a picture is very high.

These arguments could have potentially stopped Miss Vito's testimony from being admitted and made the prosecution's case against Vinny's cousin and his friend much stronger. (Although, since the prosecution's expert sitting in the gallery seemed to agree with Miss Vito, it might not have worked in that case.)

How does it work in a non-fictional courtroom?

In the real world, what you see more often is what litigators call a “battle of the experts,” where each side has a theory about the science involved in a case, and each side has experts that back up that theory. This turns the case, at least partially, into a battle between which expert the jury will ultimately believe.

Figuring out the best strategy for a trial can be difficult and daunting. The attorneys at Patriots Law Group have extensive experience litigating cases. Not only have they successfully had expert witness testimony admitted in their trials, but they have also successfully opposed the admissibility of the prosecution's expert witnesses. Give us a call at (301) 952-9000 to see how Patriots Law Group can help you with your litigation strategy.

DISCLAIMER:  The information above is for informational purposes only and is not intended to serve as legal advice for any particular situation.  No attorney-client relationship is intended or created by this information and may not be relied upon based on the above-statements.  Each individual situation is different and therefore a consultation is necessary before any advice can be relied upon as appropriate and accurate for your situation. Please call Patriots Law Group at 301-952-9000 to set up a consultation if you wish to obtain specific legal advice concerning your situation.

About the Author

Michael E. Lyons

“As a veteran, I bring my core values of service, integrity, and excellence to every client, every case, every time.” Background: Michael E. Lyons (“Mike”) handles cases in Maryland and Washington D.C. fr...


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