During a DUI / DWI criminal trial, the prosecution will call several witnesses, including the arresting officer and a prosecution “expert,” usually an employee of the sheriff’s department, who will interpret the defendant’s chemical test results, blood alcohol content (BAC), and field sobriety tests. An experienced drunk driving attorney will counteract this testimony with his or her own expert, who will demonstrate that the driver’s chemical tests can be interpreted in an entirely different way.
The use of experts is extremely important in drunk driving or driving under the influence of drugs (DUID) cases. Experts can be called to discuss a variety of topics, but their primary purpose is to support the idea that there are other possible explanations for the prosecution’s evidence that the defendant was driving under the influence. Defense experts can testify knowledgeably about scientific aspects of being under the influence, and also question the prosecution expert’s hypothetical theories and conclusions.
The direct examination of the defense expert is done much the same as other direct examinations. The DUI defense attorney asks open-ended questions that allow the expert to give the majority of the testimony. The key to this part of the DUI trial is the selection of the expert. The skilled DUI defense attorney 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. Sometimes these experts were once prosecution experts, which aids the defense because the jury sees that the crimnalist now chooses to work for the defense.
Defense experts may have access to studies and resources that are not available to the prosecution. A defense expert can also assist in the defense of a DUI / DWI case by helping prepare 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 DUI case.
The defense expert can successfully challenge a number of prosecution claims. Perhaps the most import concept the expert can explain to the jury is rising blood alcohol content (BAC). Most jurors are unaware that a person’s 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 after driving, a person’s BAC could very well be .08 percent 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.
The expert can also explain flaws in both breath and blood tests, such as the elevated readings that occur when breath machines are not properly calibrated, or when fermentation takes place in an improperly stored blood sample.
Experts can also use a driver’s performance on field sobriety tests to support their opinion that the accused motorist was not under the influence at the time of driving. The expert can use a good performance on the test to show that was no mental or physical impairment.
Mental and physical impairment are very important because any good expert will testify that mental impairment always precedes physical impairment when a person is intoxicated. If there was no evidence of mental impairment, but was some physical impairment, the poor physical performance must have been caused by something other than intoxication. The expert will explain that there are many conditions that can cause physical impairment, including illness, injury, or fatigue.
After the defense attorney examines the witness, the prosecutor begins cross-examination. As with other cross-examinations, the questions are in a “leading” form and are designed to elicit only a yes or no response. Because this is the prosecution’s opportunity to testify, just as the defense attorney did while cross-examining the prosecution expert, it is essential that the expert is well prepared for trial.
The defense attorney and the expert usually meet before the DUI trial, often several times, to go over the expert’s opinions in regards to the particular drunk driving case. They also 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.
A skilled defense criminalist can hold his or her own on the witness stand during a DUI / DWI trial. Because the expert has testified in countless other trials, he or she is well prepared, and knows the issues of drunk driving backward and forward. However, there are times when the prosecution may score a point or two with the defense criminalist due to unavoidable flaws in the case. If that happens, a good defense criminalist is able to testify in a way which leaves open the chance for the defense attorney 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 skilled and knowledgeable DUI defense expert is essential to a successful defense in drunk driving cases. A lawyer who specializes in DUI / DWI cases knows the best experts in the field and is able to select the defense expert who will have the strongest impact on the jury to create reasonable doubt in the client’s guilt.