Monder Law Group - News
DUI Expert Witness
When a DUI expert witness is involved with a case, a motion for a 402 hearing is normally requested for the defense. A 402 hearing is to determine if the evidence is admissible and to determine if the prosecution “expert” is truly a DUI expert witness in the applicable field. A defendant would also request a 402 hearing to question an officer’s qualifications regarding HGN or horizontal gaze nystagmus. A witness can also be discredited when using an opinion of guilt and intoxication for the purposes of driving.
A testimony that links a specific blood alcohol concentration to the presence of HGN would also be questioned. The officer’s ability to administer a PAS test can also be argued by questioning if the instrument was in proper working order, the test was properly administered, and the operator was competent and qualified. An officer must comply with set procedures when administering a breath test, and without proof of this being properly administered, can be argued.
The verdict of innocence or guilt is determined by the jury. It is improper for a DUI expert witness to declare this because of their suspicion of intoxication. An expert opinion generally can be put into question based on the expert’s qualifications. A DUI expert witness may not have an advanced degree in a field and solely possesses a simplistic understanding of the topic. A common witness opinion used is that all people are impaired for the purposes of driving at 0.05% BAC. There is no supporting documentation of this nor is that the law. Different BAC’s affect people in different ways. Without proper citation of that claim, the evidence should not make it to the jury.
A DUI expert witness will testify based on studies that the DUI expert witness is involved with. These studies are often times not published, and the no information about the studies is provided to the defendant. The invalidity of the studies can be argued. Unless a DUI expert witness has an advanced degree in physiology, organic chemistry, biochemistry, anatomy, or other applicable sciences, the prosecution may not be as concrete. Only the general notions of the effects of alcohol would be valid, and since this is considered common knowledge, an expert will not be able to testify that information. A DUI expert witness is not qualified to testify regarding how alcohol is processed or how alcohol tolerance plays into mental and physical impairment. The witness would be unable to provide any sort of evidence to cite this claim. Only DUI expert witnesses can give insight into hypothetical scenarios; therefore, witnesses are restricted in doing this. Situations outside a witness’s scope of knowledge, such as field sobriety tests and their effect on the determination of impairment, cannot be testified.
The qualifications of a DUI expert witness do not permit a testimony concerning the workings of the machine in question and its inner workings of determining impairment. The number of drinks correlating to the defendant’s BAC cannot be estimated by a DUI expert witness. The necessary equations and derivations are outside of the witness’s scope of knowledge. Only an extremely simplistic formula may be used, but that may be disputed due to its neglect of important variables. Often times, a DUI expert witness with an advanced degree needs to be used over a DUI expert witness because the claims of a DUI expert witness are more easily supported.