Selecting and Using Defense Experts in the DUI Trial

by Patrick T. Barone, Barone Defense Firm, Birmingham, Michigan

The following is an excerpt from the upcoming 2010 supplement to Defending Drinking Drivers:

The Selection of the Defense Expert at Trial

The expert witness has become an important member of the defense team in many drunk driving cases. Per se statutes have enhanced the importance of chemical evidence and, therefore, have often necessitated the use of expert testimony to analyze, question and rebut the state’s chemical evidence. Properly used, expert witnesses can aid the attorneys, the judge and the jury in understanding many of the crucial issues surrounding the guilt or innocence of the drunk driving defendant.

However, an attorney should never use an expert as a substitute for his or her own lack of knowledge regarding the science of chemical testing or the metabolism of alcohol. Attempting to use an expert to “fill in the gaps” of one’s own knowledge is almost sure to meet with disaster at trial. Many of the references needed to gain this knowledge are listed in the bibliography of this treatise, and there are also many excellent advanced training seminars presented throughout the country each year.

Additionally, unless the expert can make the attorneys, the judge and the jury understand his or her testimony, the expert’s reception will be disappointing. The expert witness is in a precarious position because the presentation of his or her arguments depends upon the questions of the attorney. Therefore, the framing of the questions determines to a large extent the kind and effectiveness of the expert’s answers. This is another reason why the defense attorney must have a vivid understanding the legal and scientific issues involved in the client’s case. Armed with such an understanding, the defense attorney will know how to ask questions that will produce the most helpful answers. On the other hand, uninformed and uneducated questions from counsel usually result in a reinforcement of the State’s scientific evidence.

Careful preparation requires adequate consultation between you and your expert witness. Decisions on the order of the questions, the methods of attack on the chemical evidence, the emphasis to be given certain data, possible hypotheticals and final summary questions should be made carefully. You and your expert witness should (a) agree on the purpose of the evidence to be presented, (b) have examined the essential questions that may be raised by the state in cross-examination and (c) have reduced the total presentation to brief, clear and concise argument.

Defense counsel must first be satisfied that the expert has the requisite knowledge, skill and experience to testify at trial. Defense counsel must also make the appropriate arrangements with respect to the expert’s fee and be sure that the expert will be available for consultation and trial when needed.

With a little time and effort, finding an appropriately qualified expert should not be difficult. There are many expert witness directories available on the internet. There is however no substitute for word-of-mouth recommendations. Ask other lawyers who aggressively handle drunk driving cases which experts they’ve successfully used in the past.

If your proposed expert has no track record of which you are aware, then you should consider checking the expert’s references and to verify their CV so that the expert does not embellish, fabricate or enhance his or her credentials. If you don’t verify everything, then you can bet that the prosecutor almost certainly will. Thus, when the fraud is uncovered, the testimony that you worked so diligently to perfect may cause nothing but embarrassment for you and your client. A sure-fire way path to the one-word verdict is by way of judge or jury’s opinion that your expert is not a truth-teller.

Preparing the Defense Expert for Trial

Once the expert’s credentials have been checked, and you are satisfied that the expert can help your case, the expert must be prepared for trial testimony. The following points should be considered and addressed when preparing to use an expert witness and in preparing his or her testimony at trial:

  • Well in advance of trial provide the expert with copies of police reports, witness statements, log books, maintenance records and any other information available to you that relates to the proposed area of testimony. It may also be desirable for the expert to interview the client. This will preclude a series of cross-examination questions related to the expert’s lack of personal knowledge about your client or about the facts of the case.
  • Research the law to confirm that the proposed area of testimony will be admissible and that your expert will meet the necessary standards and criteria set forth in the relevant court rules. It is your job to confirm that the expert will be qualified and in fact allowed to testify. An unsuccessful attempt to have your expert qualified is another sure-fire path to a one-word verdict.
  • It is also your job to educate the expert on such legal issues that may bear upon his or her testimony, and to simplify them wherever possible. Just as you are relying on the expert to help educate you on the science involved in your case, he is relying on you to educate him on the law involved. Doing so will help the expert cater her testimony to the specific laws in your jurisdiction.
  • Take the time to fully learn and understand the science that underlies the expert’s opinion(s). In doing so you should review any relevant scientific authorities including textbook chapters or science journal articles. After the factual and legal issues supporting your theory of the defense have been discussed and evaluated with the expert, and you are confident that you fully understand them, you must synthesize all of this knowledge with your theory of the case. You must also use this understanding to prepare your voir dire, opening statements, direct questioning, and closing argument
  • The expert’s opinions must be based upon science and not upon speculation. The expert’s opinions must also be consistent with the version of facts that you know will be presented to the trier of fact. There is no benefit to be gained in having your expert prepared to testify about a rising blood alcohol defense if the requisite facts needed to make out this defense will not be received in evidence.
  • Confirm that the expert will simplify complex scientific issues and help to educate you and the jury relative to these issues. Always help your expert find ways to simplify your defense theory and remember that Occam’s razor applies here, which is to say that the simplest explanation or strategy tends to be the best one. Metaphors are the best way to simplify otherwise complex scientific concepts, and you should work with your expert to create such metaphors to fit the facts of your case.
  • Plan both direct and cross-examination. It is probably best to avoid a plan to use specific or exact wording in the direct examination of the expert or in preparing the expert’s answers. This is because doing so inevitably creates a stilted or obviously rehearsed performance. Instead the goal is for you to spend enough time preparing the testimony of your expert that the performance appears to be spontaneous because in reality it is spontaneous.
  • Help your expert to anticipate cross-examination. Reverse roles with your meanest most tenacious prosecutor, and then cross-examine your expert as this prosecutor. Consider having a non-lawyer sit in on the preparation to offer his or her opinion about the clarity of the expert’s opinions and testimony. Modify the approach based on anything you or your assistant finds to be confusing or ineffective.
  • Instruct the expert witness to stay on topic and to not express any opinion on direct or cross-examination that is outside your theory of the case. It is also important that the expert not try to stretch his or her expertise and only to testify regarding matters upon which he legitimately has expertise. An expert that is shown to be unqualified in one area may be assumed to be unqualified in other areas and his or her credibility may be seriously questioned. There is nothing wrong with the expert expressing ignorance on a particular area, especially if it is an area that is not relevant to your defense theory.

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2 Responses to “Selecting and Using Defense Experts in the DUI Trial”


  1. 1 Harri March 2, 2010 at 5:08 am

    I found your DUI law article really interesting. I am always looking for great DUI Lawyer information. I run a list and blog for DUI Lawyers Attorneys its free to submit your information if you are a DUI Lawyer or a DUI Attorney. You can click here to get added to our directory if you are a Lawyer or Attorney just go to http://www.duilawyerlist.com and click on Join the DUI Lawyer List. It is for any state in the United States


  1. 1 DUI Expert Witnesses | DUI Help from Michigan's Leading DUI Defense Lawyer Trackback on January 7, 2010 at 10:37 pm

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