DUI Investigation

DUI Investigation

A DUI (Driving Under the Influence) investigation in California begins when law enforcement suspects that a driver may be impaired by alcohol or drugs. This can occur during routine traffic stops, sobriety checkpoints, or if an officer observes erratic driving behavior. A DUI investigation in California is a process by which law enforcement gathers evidence to determine whether a driver is under the influence of alcohol or drugs. This investigation begins as soon as an officer notices your vehicle and continues through arrest and chemical testing. Understanding each stage of a DUI investigation is crucial to defending against charges and protecting your rights.

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Vehicle Stop: The First Step

The first element of a DUI crime is driving.  In California, the prosecutor must show the driver drove a motor vehicle.  They must prove the vehicle moved while being controlled by the driver. 

Many DUI investigations begin with a vehicle stop.  An officer may pull over a driver for any number of reasons, such as swerving, speeding, or even a minor traffic violation like a broken tail light. In California, law enforcement only needs reasonable suspicion to stop a vehicle. Once the officer approaches the vehicle, the investigation continues through a series of observations.

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During the stop, the officer may look for physical signs of intoxication, such as:

• Slurred speech
• Bloodshot eyes
• The smell of alcohol or marijuana
• Difficulty finding the license, registration and proof of insurance from inside the vehicle.

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Officers often ask seemingly casual questions but are actually gathering evidence to use in court, such as asking if you’ve had anything to drink, or more aggressively, “how much have you had to drink tonight?”. Any admission can escalate the investigation and lead to further scrutiny.

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Moving from a traffic stop to a DUI investigation.  If the officer feels that the driver they stopped may be under the influence of alcohol, then the officer will likely ask the driver to step out of the vehicle so that the officer can evaluate the driver and ensure that the driver is safe to continue driving.  

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When getting out of the vehicle, the officer will be looking for difficulty getting out of the vehicle, did he need support by holding onto the door or side of the vehicle.  Did the driver stumble?

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Field Sobriety Testing: Voluntary but Risky

If an officer suspects a driver is under the influence, the officer will follow the standard procedure to conduct a DUI investigation.  This will generally begin with officers asking standard DUI investigation questions.  These questions have several purposes.  The first is to lock the driver into a particular story, and to eliminate possible defenses, or arguments about poor performance on the field sobriety tests.  For example, they ask if you have anything physically wrong with you?  If the driver says no, then it makes it difficult for the driver to later say that they have a bad knee, so that impacts the FST performance.  The officer will also ask the driver to tell them when they started and stopped drinking.  Many drivers will often lie about when they drank and how much.  Typically the driver will reduce the amount they drank, and put the time of drinking back in time (“I had two beers three hours ago”).  This lie is not going to get the officer to stop investigating the driver for a DUI, but if the driver drank more recently, the driver may have a blood alcohol level below 0.08 when they were stopped, but by the time the the driver is arrested and tested following the arrest the blood alcohol level may have surpassed 0.08, but because the driver told the officer they had not had anything to drink in over two hours, the driver’s blood alcohol level would have been going down, not up.    

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Standardized Field Sobriety Tests (SFSTs). Common tests include:

• The walk-and-turn test
• The one-leg-stand test
• The horizontal gaze nystagmus (HGN) test, which examines involuntary eye movements

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In California, field sobriety tests are voluntary, and drivers are not required by law to participate. These tests are notoriously subjective and often unreliable, as factors like fatigue, nervousness, or even medical conditions can affect performance.

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The officer may also request a preliminary breath test (PBT) using a portable breathalyzer. This test is also voluntary, and is viewed as a Field Sobriety Test, which the driver is free to decline to participate in. 

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Chemical Testing After Arrest: A Legal Requirement

Once arrested for suspicion of DUI, California’s implied consent law mandates that you submit to a chemical test—either a breath or blood test. Refusing this test can lead to severe consequences, including an automatic license revocation for a year or longer and fines, even if you were sober.

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Unlike the preliminary alcohol screening test (PAS), the chemical test taken following the arrest, are considered evidentiary in nature and admissible in Court. However, these tests are not infallible. Issues with equipment calibration, testing procedures, or even the timing of the test can lead to inaccurate results. A skilled DUI attorney can challenge these test results to help reduce or dismiss charges.

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If the driver takes a blood test following the arrest, your defense team can have the blood sample re-tested to make sure that the state’s lab results were accurate.

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The Police Report: Documenting the DUI Investigation

After gathering evidence through tests and observations, the arresting officer will write a police report detailing everything from the initial vehicle stop to the chemical test results. This report will include any signs of intoxication, such as failed sobriety tests, slurred speech, or erratic driving behavior.

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It’s critical that individuals arrested for DUI take notes on the events of the investigation as soon as possible after being released. These notes can be valuable when your attorney examines the case, looking for inconsistencies in the officer’s report or procedural errors.

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Elements of a DUI Offense in California

To secure a conviction for DUI in California, prosecutors must prove two key elements:

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1. The defendant was driving a motor vehicle.
2. The defendant was under the influence of alcohol or drugs while driving.

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Driving a vehicle may sound straightforward, but it can sometimes be a point of contention in DUI cases. For instance, if an individual was found in a parked car with the engine running, a prosecutor may argue that they were still "driving." The prosecutor has to prove that the driver’s blood alcohol level was 0.08 or higher at the time of driving, which means that the prosecutor must also prove when the driving occurred and what the blood alcohol level was at that time.  Under the influence refers to a person’s ability to drive being impaired to the point that they can no longer operate a motor vehicle with the same care and concern as a sober driver.  There is no particular Blood Alcohol Content or drug level in the driver’s system. This charge is generally proven with other types of evidence, such as circumstantial evidence and observation evidence by the officer(s).  

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If a driver’s Blood Alcohol Content (BAC) is 0.08% or higher, they are considered legally impaired under California’s per se law. Commercial drivers face stricter limits, with a per se DUI limit of 0.04% BAC or higher if driving a commercial vehicle and a BAC of 0.04 or higher if driving a Lyft or Uber with a passenger. For drivers under 21, California’s zero-tolerance policy makes any detectable alcohol in their system grounds for an DUI Under 21 and potential revocation of your driving privilege for a year or longer.  

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DUI Defense in California

Defending against DUI charges requires a thorough examination of the investigation process. A DUI defense attorney can challenge the legitimacy of the vehicle stop, the accuracy of field sobriety tests, and the reliability of chemical test results. They may also argue that the prosecutor has not met the burden of proving that the driver was under the influence or that they were driving.

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In some cases, procedural errors made by law enforcement such as failing to properly administer a breathalyzer or violating your rights during the arrest can lead to a reduction or dismissal of charges.

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If you are facing DUI charges, contact a qualified criminal defense lawyer to discuss your case and start building a strong defense.