At some point during your DUI/DWI trial, your lawyer will probably decide to call an expert to testify. Experts can be called to testify about the chemical tests, field sobriety tests, accident reconstruction, and other scientific aspects of your case.
Chemical Tests: Experts can discuss flaws with breath, blood and urinalysis tests. For example, the breath machine was not properly calibrated or fermentation occurred in the blood and a higher alcohol reading resulted.
Field Sobriety Tests: Field sobriety tests are not considered “scientific,” but the results can work in your favor if your lawyer calls an expert witness to testify on your behalf. If you performed reasonably well on the field sobriety test—displaying good balance, coordination, attention and reasoning—the expert can use your performance on the field sobriety test to support the opinion that you were not under the influence at the time of driving. If you showed signs of physical impairment but not mental impairment, the expert will testify that, because alcohol always affects your mind before your body, the physical impairment was probably due to something other than alcohol.
Alcohol Level at Time of Driving vs. at Time of Testing: The use of BAC (blood alcohol content) tests at trial is based on the assumption that, if a person was impaired at the time of the test, they must have been impaired at the time of driving. In other words, the assumption is that the BAC falls as time passes. Experts can be called to rebut this assumption in certain cases. Under certain circumstances the BAC could actually be rising, which means it is higher at the time of the test than when driving. Since this is an extremely technical area, an expert is essential to explain it to the jury and raise reasonable doubt as to whether the person was over the legal limit at the time of driving.
Accident Reconstruction: If there was an accident before the arrest, an expert in the field of accident reconstruction may be used to reconstruct the events of the accident based on facts in the case. The accident reconstruction expert can testify regarding the mechanics of the accident, and give his or her opinion regarding whether or not the accident was the fault of the impaired driver, the other party, or would have been unavoidable regardless of impairment.