How do you “suppress evidence” in a DUI case?

Posted on January 19, 2022

Defendants facing criminal charges for driving under the influence of drugs or alcohol can file a suppression motion asking the court to disregard (“suppress“) all the evidence that law enforcement officers may have unlawfully obtained. If the judge grants this motion, then the prosecution may be forced to dismiss the DUI charges for lack of proof.

What is common DUI evidence?

Ten typical types of evidence in drunk driving or drugged driving cases include the following:

1. Evidentiary blood test results that measure the defendant’s blood alcohol content (BAC) or existence of drugs in the blood
2. Evidentiary breath test results that measure that defendant’s BAC
3. Eyewitness testimony and statements
4. Video surveillance footage, police bodycam video, and/or smartphone video and photos from eyewitnesses
5. Medical records of the defendant
6. Results of the walk-and-turn field sobriety test
7. Results of the one-legged-stand field sobriety test
8. Results of the horizontal gaze nystagmus field sobriety tests (where a DUI suspect follows a pen back-and-forth with his/her eyes)¹
9. Statements the defendant made at the scene or following the Miranda rights warnings (if applicable)
10. The police report, which should include the following aspects of the DUI investigation:
    1. Why the arresting officer initiated the traffic stop in the first place (unless there was an accident, and the police arrived after the fact),
    2. whether the defendant had an odor of alcohol or marijuana,
    3. whether the defendant had red, glassy, or watery eyes, and
    4. whether the defendant had slurred speech

Note that results of the preliminary alcohol screening test – a roadside breathalyzer test administered to a DUI suspect prior to any arrest – are typically not admissible in DUI criminal trials. Their purpose is merely to help the police determine whether there is probable cause that the suspect has committed driving under the influence of alcohol.

What are the grounds to suppress evidence in DUI cases?

The primary reason that courts throw out evidence in DUI cases is that it was found through an unconstitutional police search and seizure.² Five examples of such police misconduct include:

1. The police did not have reasonable suspicion to pull over the defendant. For instance, perhaps the officer was racially profiling the driver.
2. The police administered the field sobriety tests incorrectly, such as by giving incorrect instructions.
3. The police did not administer the breathalyzer chemical test correctly, and/or the breathalyzer was not calibrated or maintained correctly.
4. The blood samples were not collected or stored correctly, there was a broken “chain of custody”, and/or the samples were contaminated.
5. The police officer did not have probable cause to ultimately execute a DUI arrest of the defendant.

Note that courts may suppress illegally-obtained evidence in a criminal case even if the evidence is otherwise relevant and suggests that the defendant is guilty, such as a BAC result that is above the legal limit. Whether the evidence is seized lawfully is more important than what it proves in a DUI case.

Police usually must get a warrant to obtain blood from a DUI arrestee who refuses to give any.³.

What is the procedure for bringing suppression motions?

While the DUI case is still in the pretrial stage, the defendant (or the defendant’s DUI attorney) files a motion to suppress evidence outlining all the legal reasons why the court should disregard certain evidence. Then the prosecutors will respond, outlining all the legal reasons why the court should admit the evidence. Then the defendant (or DUI defense lawyer) may rebut this response.

Eventually, the court may hold a suppression hearing. Both the defense and prosecution can present their arguments to the judge in open court, and the judge can ask questions of each side. In some cases, the judge decides on the bench whether to grant the motion. In other cases, the judge may take more time to think about it and issue a decision later on.

If the defendant loses the suppression motion, he/she may be able to appeal the decision to a higher court.

What is the law in California?

Suppression motions in California are called 1538.5 motions. Defendants can file these motions during the preliminary hearing (in felony cases) or at a pretrial hearing.

California law requires courts to grant suppression motions when the evidence was obtained:

1. By an unreasonable law enforcement search done without a search warrant, or
2. By a police search conducted with a warrant if either:
   1. The warrant was deficient,
   2. The evidence obtained was not described in the warrant,
   3. The warrant was not based on probable cause, or
   4. The search was executed in a way that violated the California Constitution or the United States Constitution.⁴

Defendants must prove their motion by a preponderance of the evidence. This means that it is more likely than not that the evidence was unlawfully-obtained and is therefore inadmissible at trial.⁵

Contact our law firm for a free consultation with our criminal defense attorneys. Our law offices create attorney-client relationships in Los Angeles and throughout California.

Legal References

About the Author

Neil Shouse

A former Los Angeles prosecutor, attorney Neil Shouse graduated with honors from UC Berkeley and Harvard Law School (and completed additional graduate studies at MIT). He has been featured on CNN, Good Morning America, Dr Phil, The Today Show and Court TV. Mr Shouse has been recognized by the National Trial Lawyers as one of the Top 100 Criminal and Top 100 Civil Attorneys.