PA DUI Mailbag: Why do you use Expert Witnesses

Every Friday we will take a look at some of the most commonly asked questions about Pennsylvania DUI so that we can clear up any misconceptions and provide you with the most up-to-date and accurate information.  Today:

I consulted with one of the lawyers in your firm and he recommended that we call in an expert witness to testify in my DUI case.  What is the advantage of calling in an expert?  Is it worth the extra costs?

The use of experts is extremely important in DUI and DUID cases. The prosecution will be putting on the stand the arresting officer and the person who performed the chemical test to testify as to why you are guilty. It is vital that we are able to put on our own witnesses to counter that. Although we at the McShane Firm, LLC have many advanced certificates and specialized training in the Standardized Field Sobriety Tests and chemical testing (perhaps more so than 99% of the officers/ "scientists" that the state uses), we can only act as the lawyer by asking questions, not as a witness giving answers. An attorney cannot act as both. Experts can be called to discuss a variety of topics, but their primary purpose is to support the idea that there are other possible explanations for the prosecution’s evidence.

PA DUI blood testsDUI Chemical Tests: Experts can discuss some of the many flaws associated with both breath and blood tests.  For example, the breath machine is not properly calibrated or fermentation occurred with the blood and a higher alcohol reading was the result. There are a variety of ways an expert can question the chemical tests to not only cast reasonable doubt, but sometimes can prove actual innocence.

Standardized Field Sobriety Tests: Experts can use a person’s performance of the Standardized Field Sobriety Tests (SFST’s) to support their opinion that the motorist accused of DUI was not under the influence at the time of driving. If the SFST’s are performed well, the expert can use this to show that there was no physical impairment (if there is good balance, no swaying, etc.) and no mental impairment (if the person followed instructions, counted in correct order, etc). Mental and physical impairment are very important because any good expert will testify that mental impairment always precedes physical impairment when a person is intoxicated. This means if there was no evidence of mental impairment, but there was some physical impairment, the physical impairment was probably due to something other than intoxication (such as an injury or poor testing conditions or nerves).

Most, if not all, of the cases that we see involve arresting officers who do not properly conduct the SFST’s or know what they are properly used for. According to the original research by the researchers who developed the SFST’s, if the standardized method of explaining the tests are not used and the standardized method of conducting the tests are not used, and the standardized clues of grading the tests are not used, then the results are invalid.

Accident Reconstruction: It is often helpful  to have an expert in the field of accident reconstruction. Anytime there is a DUI arrest along with an accident, the passions of the jury will likely be inflamed. As such, it is essential that an accident reconstruction expert be available to testify regarding the mechanics of the accident, and to offer opinions regarding whether or not the accident was the fault of the impaired driver, the other party, or would have been unavoidable regardless of the impairment or non-impairment of the accused DUI motorist.

As for your question of cost, here is an analogy. What if I gave you a blank check and told you that you could write it out for whatever amount you wanted but before you could cash it, you first had to undergo a loss of your driver’s license for at least twelve (12) months if not more, have two (2) counts of DUI on your record and undergo a period of actual incarceration and a substantial amount of supervision with the appropriate probation and parole office. How much would that check be?

It will be probably far less than the costs associated with the best DUI experts.

If you would like to ask a question, please submit it via the contact us link.


-Justin J. McShane, Esquire, Pennsylvania DUI Attorney

I am the highest rated DUI Attorney in PA as Rated by Avvo.com

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Harrisburg DUI Lawyer Justin J McShane NBTA certification

Board Certified Criminal Trial Advocate
By the National Board of Trial Advocacy
A Pennsylvania Supreme Court Approved Agency

PA DUI attorney Justin J. McShane is the President/CEO of The McShane Firm, LLC - Pennsylvania's top criminal law and DUI law firm. He is the highest rated DUI attorney in PA as rated by Avvo.com. Justin McShane is a double Board certified attorney. He is the first and so far the only Pennsylvania attorney to achieve American Bar Association recognized board certification in DUI defense from the National College for DUI Defense, Inc. He is also a Board Certified Criminal Trial Advocate by the National Board of Trial Advocacy, a Pennsylvania Supreme Court Approved Agency.

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