Mounting An Expert DUI Defense: Calling On Specialist Witnesses

This article provides key information about the types of expert witnesses your defense attorney could call on in court to defend against DUI charges. It includes:

• A list of experts and the topics they can testify.
• An in-depth dive into the toxicologist’s role in DUI cases.
• How some experts might also be called on or cross-examined by the prosecution.

If ever you have the misfortune to be charged, wrongfully or otherwise, for Driving Under the Influence (DUI) of alcohol or an illicit substance, then you may find yourself defending your case in court or at a DMV hearing.

If, however, you have the means to afford a DUI defense attorney, then you will not be doing so alone. In addition to providing you with legal guidance and arguing your case, you can expect your attorney to bring in as many expert witnesses are needed to help defend your case.

What Experts Can My Attorney Call To Help Defend Against DUI Charges?

There are several experts an attorney can call to assist in defending against DUI charges. Each offers specialized testimony on specific aspects of a case, which could prove invaluable in clearing your name or provide leverage to negotiate a lesser charge or penalty.

• A forensic toxicologist. Forensic toxicologists can testify about driving impairment caused by alcohol or controlled substances as well as about technical details like the manner in which government labs are required to store and maintain blood samples. Additionally, a toxicologist can testify as to the proper use of a breathalyzer and the potential unreliability or margin of error for the device. Finally, toxicologists can help your attorney mount a specific defense, such as the rising blood defense, by providing expertise as to what constitutes “rising blood”.
• A former law enforcement officer. Former law enforcement officers can make excellent expert witnesses. Typically, they are called to testify about standard law enforcement practices and procedures when detaining, arresting, and investigating charges of driving under the influence. A former law enforcement officer, if retained, can identify deficiencies in the procedures used by law enforcement which could undermine the prosecution’s case.
• A field sobriety test expert. These experts are typically certified by the National Highway Traffic Safety Administration or NHTSA. They can educate the jury about the proper way to demonstrate and perform the standardized field sobriety tests and identify tests that are not standardized, as well as the reliability and validity of roadside tests and the number of clues needed to indicate impairment on field sobriety tests. Furthermore, a field sobriety test expert can identify medical conditions that may limit someone’s ability to perform the field sobriety tests or lead to misleading results.
• An accident reconstruction expert. Accident reconstruction experts may be called in for DUI cases involving an accident, crash, or injury. Accident reconstruction experts can identify the causes of traffic collisions which can often be of vital importance in such a case.
• Breath alcohol testing experts or medical experts such as someone qualified to testify about gastroesophageal reflux disease (GERD), which may affect the results of a breathalyzer test. Typically, these would be medical doctors, internists, gastroenterologists, or surgeons. Pharmacists can also be called to testify as experts in a DUI case to explain the effect of specific substances on the human body.
• A Nurse. Nurses can testify about the proper manner to conduct a blood draw according to accepted medical practices. A nurse expert might be called on during pretrial proceedings to determine whether the blood draw in a DUI case was conducted in violation of the Fourth Amendment.

While this is not meant as an exhaustive list of all possible experts that might be called upon in a DUI case, the list offers a glimpse of the number, variety, and importance of expert witnesses.

Now let us look more closely at one type of expert witness in particular, which is among the most commonly called upon by DUI defense attorneys and prosecution alike: toxicologists.

What Is The Role Of A Toxicologist In A DUI Case?

Toxicologists are versatile and important experts, often retained by defendants for both DUI trials and DMV hearings.

In a DMV hearing or procedure, a toxicologist is generally called to testify about blood alcohol concentration. They can help determine whether or not the blood alcohol level was at, below, or above the legal limit of 0.08 at the time of driving.

In court proceedings, toxicologists are often called upon for slightly different areas of expertise. Notably, to testify about impairment by alcohol or controlled substances, or the manner in which government labs are required to store and maintain blood samples. Such testimony may be able to establish deficiencies in the testing process and thus in the prosecution’s case.

Finally, a forensic toxicologist can speak about chemical testing details. For example, whether at the time of the evidentiary chemical test, which could be the breathalyzer or the blood test, your blood alcohol level was rising and thus likely lower when you were driving. Or more generally, they can educate the jury about the proper use of a breathalyzer and any unreliability in the device(s) used in your particular case.

Can Medications Or Other Factors Contribute To A False Positive Reading In A DUI Case?

Another aspect of DUI cases toxicologists can frequently be called on to testify about is the effect of a procedure, condition, or medication on a breathalyzer or other chemical test. After all, it is very much possible for several substances or conditions to cause a false positive on a blood alcohol reading.

A variety of factors may contribute to false positives. For example, if the officer administering the breathalyzer test failed to observe the driver the minimum required 15 minutes from the moment of initial contact to the administration of the test, they may not observe the driver belch, burp or regurgitate which could otherwise contaminate the breath sample with stomach acids and provide a false positive. Regulations also require a two-minute delay between administering breath tests, which, if not respected, could result in inaccurate results. The toxicologist can also review calibration records to determine whether or not the device was reliably accurate at the time of the test.

Furthermore, a toxicologist can explain what types of chemicals might affect the reading on a breathalyzer test and provide false positives. Some of these include asthma medications, fumes or solvents, contaminants in the breathalyzer mouthpiece, or some specific medications like aspirin, antibiotics, or even cold medication.

Forensic toxicologists provide testimony based on their expertise as to which types of chemicals may affect or create false positives in the breath test results, as well as about any skewed blood test results if a sample was not properly collected, stored, or maintained.

Can A Toxicologist Work With A Defense Attorney To Change Or Challenge The Prosecution’s Case In A DUI Trial?

Typically, a toxicologist is retained initially to review the case details and any additional documentation obtained by the defense well before a trial. This might include maintenance and calibration records for the blood or breath testing devices, as well as documentation about the collection, storage, and chain of custody of the blood evidence.

This allows your DUI defense attorney to identify deficiencies in the prosecution’s case, which can then be used in a trial to challenge the charge or argue for a lesser one. During the trial, a toxicologist can then testify as to how these deficiencies or other factors may have affected the blood alcohol concentration of the reported results.

Their expert testimony about the evidence may be invaluable in reducing the charge against you or getting the prosecution’s case thrown out entirely.

Can The Prosecution Also Call A Toxicologist To Testify In A DUI Case Or Cross Examine One Brought By The Defense?

The prosecution will often also rely on a toxicologist during the trial when attempting to establish that you were impaired or driving with a blood alcohol concentration above 0.08%. Sometimes the government toxicologist will even attempt to argue that your blood alcohol concentration at the time of driving was higher than the reported test result.

An experienced and knowledgeable forensic toxicologist will be well-versed in their field and be able to answer these questions when asked by the prosecution. Nevertheless, a strong DUI defense attorney will usually address any possible weaknesses in your defense first during the direct examination of the defense toxicologist to ensure that those issues are addressed at the outset in your favor.

Indeed, the quality of an expert is only as good as the lawyer calling on them, so be sure that if or when you are charged with a DUI, you have an experienced and specialized lawyer at your side.

For more information on Experts Used In DUI Defense Cases, an initial consultation is your next best step. Get the information and legal answers you are seeking by calling (415) 728-9982 today.