Prosecutors in Los Angeles DUI cases call several witnesses, including the police officer who arrested you for drunk driving and a prosecution "expert," typically an employee of the sheriff's department who analyzed your chemical test results, (BAC), and field sobriety tests. A skilled Los Angeles DUI attorney will present your own expert to prove that your chemical tests can be interpreted in a completely different way.

Expert testimony is critical in a Los Angeles DUI or driving under the influence of drugs (DUID) case. The primary purpose of a defense expert's testimony is to explain that there are alternative explanations for the prosecution's allegation that you were driving under the influence. A good defense expert will testify knowledgably about the scientific aspects of intoxication and aggressively question the prosecution expert's hypothetical theories and conclusions.

When questioning the defense expert on the stand, a Los Angeles DUI attorney will ask open-ended questions that allow the expert to testify freely in a way that will advance your case. Selecting the right defense expert is critical in a Los Angeles DUI case. It's important to choose an expert who is very well-versed in the field and who can explain technical and scientific information in a way the jury can understand. Many top defense experts once testified for the prosecution, which gives them even more credibility with jurors.

In many cases, top defense experts can introduce studies and resources that are unavailable to the prosecution. A knowledgeable defense expert can also contribute to your defense by helping to prepare your Los Angeles DUI attorney to cross-examine the prosecution expert.

A good defense expert will successfully challenge many of the prosecutor's assertions in your Los Angeles DUI case. Perhaps the most critical concept the expert can explain to jurors is rising BAC. Most people are unaware that an individual's BAC continues to increase after the last drink is consumed.

Because chemical tests in Los Angeles DUI cases are always administered sometime after you were last behind the wheel - sometimes even an hour or more later - your BAC may have exceeded the legal limit at the time you took a chemical test, but that isn't illegal. The only relevant figure is your BAC at the time of driving, and that's very hard to pinpoint using a test taken several hours later. The prosecution expert will testify that you exceeded the legal limit while behind the wheel, and it's up to the defense expert to contradict that testimony.

A good defense expert will also explain the inherent flaws in breath and blood tests, such how an improperly calibrated breath testing machine can produce a false reading, or how an improperly stored blood sample can ferment and inflate your blood alcohol content.

A strong defense expert can also analyze your performance on field sobriety tests to demonstrate that you were not under the influence at the time of your traffic stop. The expert will point out aspects of your field sobriety test that you performed well that indicate that you were not impaired.

Mental and physical impairment is at the heart of every Los Angeles DUI charge, and a good defense expert will explain to the jury that mental impairment always occurs before physical impairment when an individual drinks alcohol. If you didn't display any evidence of mental impairment, then any physical impairment must have stemmed from something other than alcohol intoxication. The expert will explain that there are many conditions that can cause physical impairment, including illness, injury, or fatigue.

After your Los Angeles DUI attorney questions the defense expert, the prosecutor begins cross-examination. Just as when your defense expert questions prosecution witnesses, the prosecutor will ask the defense expert "leading" questions designed for only a yes or no response. This is the prosecutor's chance to testify, just as your defense lawyer did while cross-examining the prosecution expert. However, a well-prepared defense expert will successfully defuse the prosecutor's attack.

Your Los Angeles DUI attorney will meet with the defense expert before your trial to review the expert's opinions of your drunk driving case. They will discuss weaknesses in your case and aspects of the expert's testimony that the prosecutor is likely to attack. A skilled expert can anticipate any ambushes by the prosecutor.

Having a knowledgeable defense expert on your side is essential in your Los Angeles DUI case. An experienced Los Angeles DUI lawyer has strong working relationships with the best experts in the field, and will choose the expert that can best represent your interests in your drunk driving case.