California Criminal DUI Trial: Examination of Defense DUI Experts

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Prosecutors in criminal DUI trials call several witnesses, including the arresting officer and a prosecution "expert," usually an employee of the sheriff's department. The expert is there to interpret the defendant's chemical test results and blood alcohol content (BAC). An experienced California criminal DUI defense lawyer will call his or her own expert witnesses, who can interpret the driver's chemical test results in an entirely different way.

Independent experts are critically important in a criminal driving under the influence (DUI), or driving while intoxicated (DWI) trials. Their primary purpose is to provide alternative explanations for the prosecution's evidence that the defendant was driving under the influence of alcohol or drugs in a violation of California Vehicle Code Section 23152(a)(b). Defense experts testify knowledgably about scientific aspects of being under the influence, and question the prosecution expert's hypothetical theories and conclusions.

The criminal DUI defense attorney begins direct examination of his or her expert witness by asking open-ended questions that allow the expert to give the majority of the testimony. The key is in the selection of the expert. A California DUI defense lawyer must choose an expert who is knowledgeable in his or her field and who is able to explain technical and scientific information in a way the jury can understand. Some of these experts were once prosecution experts, which is an added plus - the jury sees that the crimnalist now chooses to work for the defense.

An expert witness in California DUI trial can also assist in a criminal DUI trial by preparing the defense attorney in his or her cross-examination of the prosecution's criminalist. This makes for a better defense on several fronts of the criminal DUI case.

Defense experts can contradict a number of prosecution claims. The most important concept the expert can explain is rising BAC. Most jurors don't understand that a driver's blood alcohol content (BAC) continues to rise even after he or she quits drinking. Since the chemical tests are always given after driving, sometimes even an hour or two later, a person's blood alcohol content could very well be .08 percent or greater at the police station, but that isn't against the law. The critical point is the driver's BAC at the time of driving, and that's very hard to pinpoint using a test taken several hours later. A prosecution expert will testify that the driver must have been over the legal limit the entire time, and it's up to the defense expert to refute that testimony.

Expert Witnesses also can explain problems with chemical tests, such as how elevated readings can occur when breath machines are not properly calibrated, or when fermentation takes place in an improperly stored blood sample.

Experts also can evaluate the driver's performance on field sobriety tests with the opinion that the accused motorist was not under the influence at the time of driving. The expert will use a good performance on the test to show that there was no mental or physical impairment.

Mental and physical impairment are very important concepts in driving under the influence (DUI), or driving while intoxicated (DWI) defense. The defense expert witnesses will testify that mental impairment always comes before physical impairment when it comes to alcohol intoxication. If the driver displayed some physical impairment but no mental impairment, the poor physical performance must have been caused by something other than alcohol. The expert can explain that there are many conditions that can cause physical impairment, including illness, injury, or fatigue.

Once the DUI defense lawyer has completed direct examination, the prosecutor begins cross-examination. Just like the defense attorney, the prosecutor will ask leading questions that are designed to elicit only a yes or no response. This is the prosecution's opportunity to testify, just as the defense attorney did while cross-examining the prosecution expert.

The defense expert witness usually meets with the defense attorney several times before trial to go over the expert's opinions in regards to the particular criminal DUI case. This is an opportunity to discuss any weaknesses in the case, and areas where the prosecutor is likely to attack the expert's testimony. A good expert will be able to anticipate these attacks by the prosecution.

Because the defense expert has testified in countless other trials, he or she is well prepared to discuss the issues of drunk driving. However, the prosecutor may score a point or two with the defense criminalist due to unavoidable flaws in the case. If that happens, an expirienced criminalist will testify in a way which allows the defense lawyer to rehabilitate those points on re-direct examination. The expert may be able to anticipate the cross-examination he or she will undergo, and be able to prevent the prosecution from scoring any points at all.

A knowledgeable DUI defense expert is imperative when fighting a California criminal DUI case. A California criminal defense lawyer who concentrates on DUI defense will select a defense expert witneess who will have the strongest impact on the jury and create reasonable doubt in the defendant's guilt.