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What types of evidence are used in DUI cases?

The forms of evidence used to prove guilt in a DUI case, such as the officer’s interpretations and the breathalyzer’s results, may be disputable.

Driving under the influence of alcohol in the state of California is illegal. The measure of driving under the influence is called blood alcohol content or blood alcohol level. BAC is expressed as a percentage of alcohol in the blood, denominated by the volume of blood in the sample. The illegal threshold of BAC in California is 0.08. Violations of this law may result in a conviction, which is associated with criminal penalties, including jail time, fines and other driving limitations.

Physical evidence

In a DUI case in California, the prosecution will be required to submit evidence in support of their conclusion that the driver in question was driving under the influence. Legal evidence represents the means by which an alleged fact may be established or disproven. Taking on many potential forms, evidence may be physical. For example, an opened and partially empty bottle containing an alcoholic beverage might be used as physical evidence.

Field sobriety tests

Another form of evidence may be documented or testimonial, based on, among other things, field sobriety tests. The National Highway Traffic and Safety Administration endorses a set of three field sobriety tests, which prompt the suspect to gaze from side to side, walk in a straight line and stand on one leg. Law enforcement observe people's behaviors and ability to follow directions and then use this to determine whether they are impaired.

Breathalyzer results

Another form of physical evidence is the set of results from tests using a breathalyzer device. A direct analysis of a driver's BAC would require a blood sample. Due to the challenges associated with an officer administering this procedure, BAC is analyzed indirectly, through the magnitude of alcohol in the defendant's breath.

This method of measuring BAC is not foolproof, however. For example, the presence of some foreign substances containing alcohol in the defendant's mouth at the time of the test could influence results. Mouthwashes and other products designed to freshen breath may contain alcohol and, consequently, influence the BAC produced by a breathalyzer device. In addition, breathalyzers are imperfect devices operated by imperfect people, creating the possibility of glitches or human error.

Value of legal defense

Multiple forms of the evidence used by the prosecution may rely on the observations and interpretations of the arresting officer. Plausible alternative interpretations of the officer's observations might weaken the case against the defendant. Furthermore, potential deficiencies associated with a chemical test, such as those administered with a breathalyzer device, might result in disputable results.

Drunk driving can be consequential not only financially, but also personally, socially and professionally. For these reasons, obtaining a legal defense team may be a priority for those charged with a DUI.

Keywords: DUI, drunk driving, breathalyzer, field test

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