“Lack of Probable Cause” as a Defense to DUI in Nevada

For police in Nevada to make a lawful DUI arrest, they must have probable cause to believe the suspect is driving under the influence. Police will point to factors such as bad driving, physical symptoms of intoxication, poor performance on field sobriety tests, and a driver’s admission that he or she has been drinking.

“Probable cause” means that a reasonable and cautious police officer would have a rational basis to believe that you drove:

1. while under the influence of alcohol or drugs, or
2. with a blood alcohol concentration (BAC) of .08% or higher.

If we can show the officers in your case lacked sufficient probable cause to arrest you, the prosecutors may agree to dismiss your case due to police misconduct. This is true even if you were technically under the influence at the time.

In this article, our Las Vegas DUI lawyers will address the following key issues regarding probable cause in Nevada DUI cases:

• 1. Traffic Stops
• 2. DUI Investigations
• 3. Probable Cause of DUI
• 4. Challenging Probable Cause
• Frequently Asked Questions
• Additional Reading

1. Traffic Stops

Police may pull you over in Nevada when they have reasonable suspicion, which is a lower standard than probable cause.

Reasonable suspicion is when there are specific facts that would lead an officer to suspect you are committing or have committed a traffic infraction or crime, whether related to drunk driving or not. In fact, many DUI arrests stem from traffic stops for non-DUI reasons such as expired tags or broken taillights.

The only exception to the reasonable suspicion requirement is DUI checkpoints, which is where every driver going through the checkpoint gets stopped. The U.S. Supreme Court has held that sobriety checkpoints do not violate the Fourth Amendment as long as they conform to certain standards of fairness and objectivity.¹

2. DUI Investigations

Once police pull you over, they may proceed with a DUI investigation if they have reasonable suspicion that you may be under the influence. Typical signs are:

• an erratic driving pattern (such as weaving, swerving, driving too slowly, making wide turns, and other traffic violations);
• you fumble when producing your license and registration;
• your speech is slurred;
• you admit that you have been drinking or came from a bar;
• there are drugs, drug paraphernalia or alcohol visible inside your car; and/or
• you exhibit physical symptoms of inebriation (such as bloodshot, glassy eyes and the odor of alcohol or marijuana).

For example, simply having a lapsed registration or no insurance should not give the officer reasonable suspicion you may be impaired. You have to display some kind of behavior that indicates impairment.

If an officer reasonably suspects you are a drunk driver (or drugged driver), they may detain you for an investigation. In Nevada, this typically involves:

• questions about where you have been and whether you have been drinking or using drugs;
• a preliminary breath test (PBT) on a handheld breathalyzer;
• one or more field sobriety tests (FSTs); and/or
• a search of your vehicle (if you consent, which we do not recommend).

With each phase of the DUI– the stop, the investigation and then a possible arrest—there is a higher standard for proceeding.

3. Probable Cause of DUI

In Nevada, your arresting officer must be able to articulate the exact facts that led them to have probable cause that you were driving under the influence. Examples include:

• you failed the preliminary breath test;
• you failed one or more of the field sobriety tests; and/or
• drugs or alcohol were in your car.

The officer will not necessarily explain to you at the time of your arrest the basis for their probable cause. However, it should be contained in the police report.⁶

4. Challenging Probable Cause

Here at Las Vegas Defense Group, we have represented literally thousands of people charged with driving under the influence of drugs or alcohol. In our experience, the following six arguments have proven very effective at showing the police lacked probable cause to make a DUI arrest:

1. You were pulled over for an unlawful reason (such as your race).
2. You did not display any signs of intoxication.
3. You passed the preliminary breath test.
4. You passed the field sobriety tests.
5. There are obvious, non-alcohol-related reasons to explain your intoxicated-like behavior, such as being tired or nervous.
6. The police search of your car was unconstitutional.

Motions to Suppress

If the police pulled you over or began to investigate you for DUI without “reasonable suspicion” – or if they arrested you without “probable cause” –  we would file a motion asking the court to suppress (disregard) any evidence the police obtained. The logic is that since the original stop, investigation, or arrest was illegal, so too is any evidence the police then found.

If the court agrees and suppresses the state’s evidence (which may even include failing blood test or breath test results), the prosecution could be left with too weak a case to continue prosecuting. They may then agree to drop your charge or reduce it to a lesser charge as part of a plea bargain.

In practice, Nevada judges are reluctant to suppress evidence for lack of probable cause in DUI cases. However, it often makes sense to file a motion anyway. As Las Vegas DUI defense lawyer Michael Becker explains:

“A motion to suppress evidence presents an opportunity to cross-examine your arresting officer. We can often discover weaknesses in the district attorney’s case and use them to negotiate reduced charges or even get them dismissed outright.”

Frequently Asked Questions

Can police stop me for a non-DUI traffic violation and then investigate me for DUI?

Yes. In Nevada, the officer’s original reason for the stop does not have to be DUI-related. A minor traffic violation, such as speeding, expired registration, no license plate, weaving, or failing to signal, can justify the stop. If the officer then observes signs of impairment, the stop can become a DUI investigation.

What driving behaviors can create reasonable suspicion for a Nevada DUI stop?

Common examples include weaving, drifting, straddling a lane line, swerving, almost hitting another object, stopping too far from the curb, making jerky stops, accelerating or braking for no clear reason, failing to signal, or sitting through a green light. However, slow driving alone is not always enough unless there are additional suspicious facts.

What are “post-stop cues” in a DUI investigation?

Post-stop cues are things officers observe after pulling you over, such as fumbling for your license, slurred speech, red or watery eyes, the odor of alcohol, trouble following instructions, admissions of drinking or marijuana use, or visible alcohol bottles or marijuana remnants in the car. These facts may help support probable cause when combined with other evidence.

Can a lawful traffic stop still lead to an unlawful DUI arrest?

Yes. A legal stop does not automatically justify a DUI arrest. The officer must develop additional facts showing probable cause that you were driving under the influence of alcohol, marijuana, prescription drugs, illegal drugs, or a combination of substances.

Do Nevada DUI checkpoints require individualized reasonable suspicion?

No. Unlike ordinary traffic stops, properly conducted DUI checkpoints do not require individualized reasonable suspicion for every stopped driver. However, police still need sufficient facts before expanding the encounter into a DUI investigation or arrest.

Can field sobriety tests and a preliminary breath test create probable cause?

Yes. Poor field sobriety test performance and a preliminary breath test result over the legal limit can help establish probable cause. In Nevada, preliminary breath test results are generally used to show reasonable grounds for arrest, not to prove guilt at trial.

What happens if I refuse a preliminary breath test in Nevada?

If you refuse a preliminary breath test, the officer must arrest you if reasonable grounds otherwise exist and take you for a reasonably available evidentiary breath or blood test. Nevada law says the PBT result may not be used in a criminal case except to show reasonable grounds for arrest.

Can DUI test results be thrown out even if the test shows alcohol or drugs?

Yes. Chemical test results may be suppressed if police lacked reasonable suspicion, lacked probable cause, failed to follow proper testing procedures, or failed to obtain a valid warrant when required. If key evidence is suppressed, the prosecutor may have to reduce or dismiss the charge.

Additional Reading

For more in-depth information, refer to these scholarly articles:

• Probable Cause, Probability, and Hindsight – Journal of Empirical Legal Studies
• Putting Probability Back into Probable Cause – Texas Law Review
• Probabilities in Probable Cause and Beyond: Statistical Versus Concrete Harms – Law and Contemporary Problems
• Probable Cause Pluralism – Yale Law Journal article on the complexities of the probable cause standard.
• Probable Cause Revisited – Stanford Law Review article discerning how probable cause operates.

Legal References: