After examining the arresting police officer at a California driving under the influence (DUI) criminal case, the prosecution typically will then call an expert from the crime lab. The expert is generally a forensic toxicologist who will begin by testifying as to his or her education and training. From there, the expert will testify as to what the breath or blood test results were and explain what they mean. The expert may also go on to testify as to how the breathalyzer (if used) was calibrated and maintained, what procedures were followed, and how any blood tests were administered and the sample preserved. The honesty and accuracy of this expert’s testimony is a critical factor during a California DUI case. Unfortunately, not all experts are objective or totally honest in their testimony. Many are trained to accommodate what the prosecution needs for them to say.
Additionally, these experts almost always testify as to what they feel the California DUI defendant’s level of intoxication was while driving, which is typically based on very broad scientific principles and assumptions. Unfortunately, these generalities and assumptions do not take into consideration the CA Drunk Driving defendant’s personal tolerance level, weight/size, absorption rate, or what he or she may have eaten prior to drinking. Prosecution experts may also be asked to testify as to how field sobriety tests assist the police in determining whether or not a driver is intoxicated. The problem is that these experts most likely were not present when the DUI defendant performed field sobriety testing and thus, are unable to state definitively whether or not the DUI defendant failed. A skilled California DUI attorney can often (under cross-examination) get these experts to admit that other things may have caused the DUI defendant to be unable to perform certain field sobriety tests or aspects of field sobriety tests.