DUI Investigation

The Investigation

A DUI investigation may begin from the moment a police officer notices your car. There are a number of signs and signals which may alert a law enforcement officer that a driver may be under the influence of alcohol or drugs. Any one thing alone may not be enough to convince a judge or jury that the driver was driving while intoxicated, but the purpose of an investigation is to put all the parts together to help the prosecutor paint a picture of a drunk driver in order to gain a conviction.

Vehicle Stop

It all starts with the observation of a vehicle. Any number of things may lead an officer to suspect a driver is drunk, but he/she only needs one reason to pull over the car in the first place before continuing the investigation. It could be something as minor as a broken tail light, a cracked windshield, or failing to signal before turning. As soon as the officer has a justification to stop the car, he/she can do so.

The investigation continues by approaching the vehicle. The officer may look for signs of impairment when first approaching the driver. The police usually asks for a driver’s license, insurance or registration. Even if he/she appears to be making small talk, it may all be part of an evidence gathering strategy. The officer may ask outright whether the driver was drinking. Any admission to drinking will likely give the officer the reason he or she is looking for to further a DUI investigation.

The officer, all the while will be looking for physical signs of impairment, such as slurred speech, bloodshot eyes, or trembling hands. The officer may also look for open containers in the car or evidence of drugs. The smell of alcohol or marijuana may be another indicator that the driver may be drinking or doing drugs.

Field Sobriety Testing

If there are signs of impairment, alcohol or drugs, the officer may ask the driver to step out of the car to perform field sobriety tests. Whatever indication the officer offers that the driver will go to jail if tests are refused, in all likelihood the officer was already planning to make an arrest. It is highly likely the officer is only looking to gather more evidence to use against the driver. Field sobriety tests are not required in California, and due to the subjective nature of the tests, they may not be recommended.

The generally accepted standardized field sobriety tests (SFSTs) include the walk-and-turn test, the horizontal gaze nystagmus test (eye test), and the one-leg-stand test. All of these tests have problems and none are 100% accurate. A sober person could fail all three just as a drunk person could pass all three.

An officer may also ask of a driver to take a preliminary breath test, also known as a field breathalyzer. This is also voluntary, and these field units are much less accurate than the chemical testing machines at police stations. Regardless of a refusal or passing a breathalyzer or SFST, the police may still decide to make an arrest.

Chemical Testing After Arrest

When the police arrests a person on suspicion of drinking and driving, they will have the driver submit to a chemical test. Unlike the field breathalyzer, this test is not voluntary. Under California’s implied consent law, refusal to submit to a chemical test will automatically result in a suspended license, even if the driver is completely sober.

The chemical breath or blood test is usually the last piece of evidence gathered in most DUI investigations. After that, the police will write up a report, recording the officer’s recollection of what happened from the time he/she first observed the driver through the arrest, noting any signs of impairment, failed sobriety tests, and blood alcohol level.

After a driver is released following their DUI arrest, it is important to record as much as he/she can remember about what happened during the entire investigation, including what the officer said and did. This way, when the driver’s DUI lawyer does their own investigation of the arrest, he/she can look for inconsistencies, improper procedures and other problems that will help dismiss the case or have the charges reduced.

Elements of the Offense

An arrest for a DUI is different than a conviction. In order for the prosecutors to prove their case against a driver, they have to show that all of the elements are met. For a first offense DUI, this includes showing:

  • a person was driving a vehicle; and
  • that person was under the influence of any alcoholic beverage or drug, or a combined influence of alcohol and drugs.

This means a driver cannot be convicted of a DUI if the prosecutor cannot prove that he/she was under the influence, or that he/she was not driving a vehicle. What is considered a vehicle? What does “under the influence” mean? While “driving a vehicle” and “under the influence” may seem like common terms that don’t need much explanation, through legislation and case law developments, just about any situation imaginable has been addressed to inform DUI cases.

If you are facing a DUI, and you have an experienced Law Firm DUI lawyer in San Jose and 10 other locations on your side, he/she will investigate your case to question the prosecutor’s case. If your lawyer can raise a doubt about any of the elements, a jury may not find you guilty of a DUI. In this case, it would include providing a defense where you weren’t driving, or not under the influence of alcohol or drugs.

DUI Defense Lawyer

Prosecutors may try thousands of DUI cases over their career, therefore they know what they have to do to win a conviction and give you a criminal record. If you want a chance to fight back against a DUI charge, you may want to have a lawyer on your side with even more experience fighting DUIs. Your experienced DUI defense lawyer will explain the elements of the crime and all possible legal defense strategies to make sure you don’t lose your license and end up with a DUI on your criminal record.


In most DUI cases, the prosecutor proves the individual was “driving a vehicle” by having the arresting officer testify, or by using the arresting officer’s report to recount the events, such as the police seeing the vehicle, turning on the sirens to pull over the vehicle, and approach the vehicle where the driver was behind the driver’s seat. However, there are many situations where it isn’t quite clear whether the individual was “driving a vehicle.”

Driving a vehicle usually involves what most of us do behind the wheel every day. A person is driving when he/she intentionally causes it to move by exercising actual physical control over the vehicle. Even the slightest movement may be enough to be considered driving. However, does it count as driving even when the car is standing still? In some cases, the answer is yes. Driving can be shown through circumstantial evidence, such as where the driver is in a vehicle, which is parked, but the engine is still running.

While most of us get around in a car, van, truck or even motorcycle, just about any kind of motorized transportation can be considered a vehicle for the purposes of a DUI. A vehicle is defined as “a device by which any person or property may be propelled, moved, or drawn upon a highway, excepting a device moved exclusively by human power or used exclusively upon stationary rails or tracks.”

In past cases, people have been arrested for a DUI in all kinds of vehicles, including a school bus, commercial truck, moped, trash truck, RV, all-terrain vehicle, and even golf carts. While a bicycle is not considered a vehicle, a bicyclist under the influence of alcohol can still be charged under California Vehicle Code 21200.5.

Under The Influence

A criminal prosecutor usually shows that the driver was under the influence through a variety of ways. This includes the police officer’s observation of how the driver was driving, the appearance of the driver, field sobriety tests, and chemical tests.

“Under the influence” is described as drinking or consuming an alcoholic beverage, and/or taking a drug that results in a driver’s mental or physical abilities to be so impaired that he/she is no longer able to drive a vehicle with the caution of a sober driver, using ordinary care, under similar circumstances.

While the police officer will report how he/she observed the vehicle, including any swerving, speeding, failing to signal, etc., the way a person drives is not enough by itself to establish whether the person is under the influence. However, it is a factor to be considered in deciding whether the person was under the influence.

Observations of the driver may also be used to decide whether he/she was under the influence. This includes things like the smell of alcohol on the driver’s breath, slurred speech, open alcohol containers in the vehicle, bloodshot eyes, or coordination problems.

Standardized field sobriety tests (SFSTs) are purported to be useful in identifying intoxicated drivers, but these tests are not always accurate and can often be misleading. This includes the walk-and-turn test, one-leg-stand test, and the HGN eye test (horizontal gaze nystagmus).

The other way prosecutors try and prove a driver was under the influence is through chemical testing. This usually involves a breath or blood test when alcohol is suspected, or a blood or urine test when drugs are suspected. Again, these devices are not 100% accurate and depend on proper calibration and operation. The results can even be compromised by operator error.

Per Se Charge

A driver is considered to be under the influence “per se” if his/her blood alcohol content (BAC) meets a certain threshold. That means that even if the driver is able to drive perfectly and there is no observable impairment to his/her mental or physical abilities, the driver can be considered impaired as a matter of law.

For most drivers, the per se limit is 0.08% BAC. If a driver’s BAC is 0.08% or higher, as tested by a chemical test of their blood or breath, then he/she will be considered impaired and charged with a DUI. In these cases, the prosecutor may only have to present evidence of the breath or blood test for the jury to find the driver guilty of a DUI. This is where an experienced DUI lawyer can call the results of the test into doubt in order to avoid a DUI conviction.

Commercial drivers have a per se DUI limit of 0.04% BAC, half of that of a regular licensed driver. For driver’s under the age of 21, the per se limit is much lower. California has a zero-tolerance policy when it comes to underage drinking and driving. Any detectable amount of alcohol in an underage driver’s breath or blood may lead to a DUI arrest. This means that even half of a light beer may result in an under-21 DUI.

Testing over the limit will also result in the DMV suspending your license. The only way to avoid an automatic suspension after a DUI arrest is by requesting a formal hearing. Your DUI attorney in Riverside, CA and 10 other locations can schedule an administrative per se (APS) hearing with the DMV, and represent you during the proceeding so that you can keep your license to drive. However, you only have 10 days after your arrest to request an APS hearing, or your suspension will automatically happen after 30 days.