Examination of a Prosecution Expert

After a prosecutor calls the arresting officer to testify in a California DUI / DWI trial, the second witness is usually an analyst from the crime lab - their "expert." The prosecution expert's testimony always supports the theory that the defendant is guilty, but an experienced drunk driving criminal defense lawyer from The Kavinoky Law Firm will aggressively cross-examine the expert and call defense experts who will contradict the prosecution witness's testimony.

The prosecution will typically begin by having the analyst describe his or her education and training in an effort to build credibility. The expert may then discuss how field sobriety tests help an officer to determine whether a driver was under the influence. The expert may then offer an opinion as to how well the defendant performed on the tests and what this says about the driver's blood alcohol content (BAC).

Prosecution experts typically make presumptions about the defendant's level of intoxication that are based on general scientific principles and assumptions. However, these assumptions don't consider a defendant's tolerance level, size, absorption rate, or meals eaten prior to drinking. The expert will describe any chemical tests the driver took, including how they were performed, the accuracy of the tests, and what this says about the level of alcohol in the defendant's system.

The prosecutor might ask the expert to describe how alcohol affects an individual mentally and physically, and to cite specific examples of behavior that show that an individual was under the influence of alcohol or drugs.

Finally, the prosecution's expert may make statements about hypothetical situations or drivers, and use these situations and conclusions to support the charge that the defendant in this specific drunk driving trial was also under the influence. Experts in driving under the influence cases can rely on hearsay evidence (out of court statements offered to prove the truth) in forming their opinions and conclusions.

Because a prosecution expert can make hypothetical assumptions about a the based on hearsay, it's essential to the defense of a driving under the influence charge that the person accused retain a qualified and experienced DUI criminal defense attorney.

After the prosecutor directly examines his or her expert, the defense attorney has a chance to cross-examine the witness. A skilled DUI / DWI lawyer will use this opportunity to discredit the expert and punch holes in the prosecutor's case. Like a defense lawyer's cross-examination of the arresting officer, grilling the prosecution's expert in a driving while intoxicated trial is less of an examination than a chance for the defense attorney to testify.

An experienced defense lawyer will ask leading questions designed to elicit only a yes or no answer. This technique allows the defense attorney to testify to what he or she wants the jury to hear, and then forcing the prosecution's witness to agree with that testimony.

An effective DUI / DWI defense attorney knows that scoring points with the prosecution's expert is even better than scoring points with the defense expert. Jurors know that the defense expert has been hired by the defense to help the defense. But the prosecution's expert is there to help convict the accused drunk driver, so persuading that witness to agree with the defense, or support something that helps the defendant's case, is much more valuable than anything the defense expert could say.

A savvy DUI / DWI criminal defense lawyer will use cross-examination to get the expert to admit that he or she doesn't know anything about the accused driver's drinking patterns, level of tolerance, or how his or her body absorbs alcohol. The expert has no information about how the defendant drank the night he or she was arrested, or how much. The expert has no way of knowing whether the driver has any injuries or illnesses that would impact the performance of field sobriety tests, or could affect the sample provided during the chemical tests.

Without aggressive cross-examination by a California defense lawyer experienced in drunk driving cases, the prosecution's expert will only offer testimony that will help convict the driver. During a skilled cross-examination, the impact of a prosecution expert's testimony can be diminished or completely eliminated.