Using an Expert in Your Pennsylvania DUI Defense

Drunk driving cases in our Commonwealth often involve scientific evidence in the form of breathalyzer or blood testing analysis. Lay witnesses (non-experts) aren’t permitted to draw conclusions or opinions on facts introduced into evidence during the course of a trial. In Pennsylvania, however, like other jurisdictions, such as New Jersey, experts are permitted to offer opinions and conclusions on matters within the expert’s field or knowledge.

An expert witness possesses scientific, technical, or other specialized knowledge beyond that of a lay person which allows them to do so. There’s no specific educational experience requirement for an expert but only that a person have “a reasonable specialized knowledge” on the subject at issue. Pennsylvania Rule of Evidence 702 allows the use of an expert during a trial if it will assist the trier of fact (judge or jury) to understand the evidence or determine a fact in issue. In addition, experts are permitted to educate the trier of fact about scientific or technical principles relevant to the case. If an expert is used, however, he or she must express their opinion within a reasonable degree of certainty (i.e. medical, scientific, etc.)

Experts in DUI cases can come from a variety of medical and scientific backgrounds; they can take the form of medical doctors, biologists, pharmacists, chemist, toxicologist and even physicists. They must, however, regardless of their education, be familiar with the particular testing technique and be able to comment on the scientific technique used or lack thereof.

While specific academic credentials are usually essential for an expert, an overly impressive academic background doesn’t necessarily mean that an expert possesses relevant knowledge to offer an opinion on matters such as alcohol absorption, chemical technical processing, and infrared spectrometry.

If your DUI case needs an expert this person’s fees will be separate from your criminal defense’s attorney fee. When your DUI attorney works with an expert, it’s obviously important that they explain the theory of defense to him or her to ensure appropriate testimony that accurately addresses the defense’s issues. When presenting issues to an expert, however, it’s import that the attorney presents the facts in terms of a hypothetical situation and avoids identifying facts set for in writing with the client. Written communication with an expert is potentially discoverable, meaning that the defense has an obligation to provide the ADA with a copy of it.

Your criminal defense attorney should never put anything in writing with an expert that could damage your case. A criminal defense lawyer, therefore, should avoid any admissions regarding the following: drinking, amount and type of alcoholic beverage (wine, beer, liquor) consumed, whether the beverage was consumed on an empty stomach or meal, the length between drinking and the arrest.

In addition, it’s extremely important that a criminal defense lawyer avoid putting in writing the type of testimony he or she is seeking from the expert (“What we are looking for is testimony that ….”). Expert testimony can be a critical part or any DUI criminal defense but it’s important that a lawyer work with the expert prior to trial to avoid hurting the case rather than helping it. For more information on drunk driving defense, I encourage you to read my monthly newsletter, the 2nd edition of my drunk driving book and watch my videos.