Expert witnesses serve a powerful role in DWI litigation. Many DWI cases frequently involve complex scientific, technical, and specialized issues which require expert testimony to assist a judge or jury’s fact-finding. The Federal Rules of Evidence relate to admissibility of expert witness testimony and the material on which experts can rely in court. According to these rules, expert witness testimony is admissible in court when: a) the expert’s scientific, technical, or other specialized knowledge can “help the trier of fact to understand the evidence or to determine a fact in issue”; b) the testimony of the expert is “based on sufficient facts or data”; c) the testimony of the expert is “the product of reliable principles and methods”; and d) the expert has “reliably applied the principles and methods to the facts of the case.

In DWI cases, expert witnesses can be helpful in attacking the chemical tests involved, establishing a defense related to the metabolism of alcohol or drugs, and discussing the propriety or impropriety of the field sobriety tests (or any other aspect of the investigation) and accident reconstruction.

In DWI cases, expert testimony can be crucial to the defense. A qualified expert can help recreate the driver’s drinking and eating pattern on the night they were arrested and offer evidence about the driver’s actual blood/breath ratio. An expert in a DWI case can estimate the blood alcohol content of a driver by looking at the particular facts involved in the case.

There are three main types of experts generally used in DWI cases. First, there are pharmacologists or toxicologists who testify about the effect of alcohol on the body at trial. Second, there are engineers who testify about the operation and reliability of the breath testing equipment used at the time of the arrest. Third, if a blood or urine test was administered, a chemist may testify to challenge the state’s use of such tests. If a breath test is at issue in a DWI case, the defense will generally establish that the expert witness is familiar with the type of breath test instrument in question, explain how the instrument works, and discuss the types of errors that the particular kind of instrument is prone to make.

An expert witness who is a chemist might be used by the defense in a DWI case to give his expert opinion about the driver’s BAC at the time of the offense by giving an estimate of the alcohol consumed by the driver before the arrest.

The police officer who made the arrest in a DWI case often serves as an expert witness and may testify about a driver’s results on field sobriety tests. The officer may be asked to testify as to specific behavior or actions of the driver that indicated that the driver was impaired by alcohol. There are many questions about the reliability of field sobriety tests. There are also questions about whether police officers are fully skilled enough to make a determination as to whether a driver is actually intoxicated or not. In court, the testimony of the arresting police officer may be attacked regarding the results on field sobriety tests on the grounds that a driver’s failure on the tests was the result of a lack of coordination and not intoxication. The defense in a DWI case may question the police officer in the case as to whether he had a reliable amount of knowledge about the driver’s intoxication and may bring up the fact that the officer’s decision to make an arrest was based on merely subjective factors.

The attorneys at the law firm of Nave DWI Defense Attorneys are experienced in handling DWI cases. If you need a lawyer who can help you obtain the best possible outcome in your DWI case, call the law firm of Nave DWI Defense Attorneys.

The exclusive purpose of this article is educational and it is not intended as either legal advice or a general solution to any specific legal problem. Corporate offices for Nave DWI Defense Attorneys are located at 432 N. Franklin Street, Suite 80, Syracuse, NY 13204; Telephone No.: 1-866-792-7800. Prior results do not guarantee a similar outcome. Attorney Advertising.