Was Your Traffic Stop Legal? How a Motion to Suppress Can Get Your DUI Dismissed

Before the breathalyzer, before the field sobriety test, before any of it — the officer needed a legal reason to pull you over. If they didn't have one, everything that followed may need to go.

By Sophie C. Bidet  ·  Criminal Defense Attorney  ·  Law Office of Sophie C. Bidet

If you've been charged with a DUI, you might assume the evidence against you is airtight. The officer pulled you over, you blew into the breathalyzer, and now here you are. Case closed, right?

Not necessarily. One of the most powerful, and most underused, tools in a DUI defense is something called a motion to suppress evidence. In the right circumstances, it can result in the entire DUI charge being dismissed before the case ever goes to trial.

Here's how it works, in plain terms.

It Starts With the Stop Itself

Under the Fourth Amendment to the United States Constitution, law enforcement cannot simply pull you over because they feel like it. A traffic stop is a seizure — and the Constitution requires that every seizure be legally justified.

To pull you over, an officer must have what the law calls "reasonable articulable suspicion"; which is a formal way of saying they need a specific, concrete reason to believe you may have broken the law. A gut feeling doesn't count. A hunch doesn't count. The officer must be able to point to specific facts they observed that gave them reason to stop your vehicle.

In DUI cases, reasonable suspicion might include things like: weaving between lanes, running a red light, driving without headlights at night, or nearly striking another vehicle. These are observable facts. They give the officer a legal basis to stop you.

But what if none of those things happened?

"The officer needed a legal reason to pull you over before a single test was administered. Without that reason, the entire traffic stop may be unconstitutional ; and everything that came after it potentially inadmissible."

What Happens When the Stop Was Illegal

Here's where it gets important for your case. There is a legal principle called the "fruit of the poisonous tree" doctrine. The idea is simple: if the tree is poisoned — meaning the initial stop was unlawful — then the fruit that grew from it (the breathalyzer result, the field sobriety test, the officer's observations, the arrest itself) is also tainted and cannot be used against you.

In other words, if the officer did not have reasonable suspicion to pull you over, then everything they discovered after the stop ( no matter how incriminating ) may be legally off-limits. The prosecution cannot build a case on illegally obtained evidence.

This is where a motion to suppress comes in.

What Is a Motion to Suppress?

A motion to suppress is a formal legal request filed by your defense attorney asking the judge to throw out, "suppress," evidence that was obtained in violation of your constitutional rights.

Think of it as your attorney standing up and saying to the court: "Before we even talk about what this evidence shows, we need to talk about how it was obtained. And the way it was obtained was unlawful. So the jury should never see it."

If the judge agrees and grants the motion, the prosecution may suddenly find themselves with very little left to work with. No breathalyzer result. No field sobriety test. No officer testimony about your condition during the stop. At that point, the prosecution often has no choice but to dismiss the charge entirely.

How the Process Works: Step-by-Step

Step 1

Your attorney reviews the police report and dash cam footage

The first thing a good defense attorney does is scrutinize exactly what the officer wrote down as the reason for the stop — and then compare it to any available video evidence. Sometimes the stated reason simply doesn't hold up.

Step 2

The motion is drafted and filed with the court

If the attorney believes the stop was unlawful, they draft a written motion to suppress. This document explains to the judge, with legal authority, exactly why the stop violated the Fourth Amendment and why the evidence must be excluded.

Step 3

A suppression hearing is held

The judge holds a hearing — think of it as a mini-trial just on this issue. The arresting officer typically testifies about what they observed and why they made the stop. Your attorney cross-examines the officer and challenges the stated justification. This is often where cases are won or lost.

Step 4

The judge rules

If the judge finds that the stop was not legally justified, the motion is granted. The evidence obtained from that stop is suppressed — removed from the case — and the prosecution cannot use it. Faced with no usable evidence, the prosecution will frequently move to dismiss the charge.

Common Reasons a Traffic Stop May Lack Probable Cause

Your stop may have been unlawful if the officer pulled you over because of:

• Vague or subjective observations, such as "driving too carefully" or "looking nervous" — without any actual traffic violation

• An anonymous tip that was not independently corroborated by the officer's own observations

• A mistake of law — meaning the officer believed you violated a traffic law that you actually did not violate

• Racial profiling or pre-textual stops where the stated reason does not reflect the actual reason for the stop

• A checkpoint that was not conducted in compliance with strict legal procedures governing sobriety checkpoints

• The officer's observations were inconsistent with what dashcam or bodycam footage actually shows

  
  

Real Cases, Real Results: What This Looks Like in Practice

The best way to understand how a motion to suppress works is to see it in action. The following are two recent examples from my own practice where the court agreed that the officer lacked probable cause — and the DUI was dismissed as a result.

I want to be straightforward: not every motion to suppress succeeds. I have handled many of these motions over the course of my career, and some have been unsuccessful. The outcome depends entirely on the specific facts of each case. But these two examples show how genuinely thin a stated justification can be — and what happens when we hold the government to its constitutional obligations.

Case 1: The Prayer Beads

My client was driving when an officer pulled him over. The officer's stated reason: a string of prayer beads hanging from the rearview mirror was allegedly obstructing my client's view of the road — a violation that, if true, would give the officer legal grounds for the stop.

There was one problem. The beads were less than two millimeters wide. At the suppression hearing, we demonstrated to the court — with evidence — that the officer's characterization of the beads as a meaningful obstruction was simply not accurate. An item that narrow, hanging from a mirror, does not meaningfully obstruct a driver's forward view in any practical sense.

The court agreed. The officer's stated justification did not hold up to scrutiny, and the court found that probable cause for the stop had not been established. Without the stop, there was no case.

Outcome: Motion to suppress granted. DUI charge dismissed.

Case 2: The Parking Lot and the Dome Light

My client was parked in an empty parking lot late at night. He was not driving. He was not weaving. He was not violating any traffic law. An officer approached the vehicle and, when contact was made, initiated a DUI investigation that ultimately led to an arrest.

The officer's stated justification for the encounter: the dome light inside the vehicle was off when the officer approached. In the officer's view, a turned-off dome light in a parked car at night was a signal that something criminal might be occurring.

We argued — and the court agreed — that this simply does not rise to the level of probable cause or even reasonable suspicion. There is nothing inherently suspicious about a parked car with its interior light off. The overwhelming majority of parked cars at night have their dome lights off. That observation, standing alone, gives an officer no legal basis to initiate a detention.

Outcome: Motion to suppress granted. DUI charge dismissed.

What both of these cases have in common is that the officer's stated reason, when examined carefully, could not bear the weight of constitutional scrutiny. That examination only happens if someone is looking for it; and most people charged with a DUI never think to look.

This Is Not a Technicality; It Is the Law Working as It Should

People sometimes hear about a DUI being dismissed on a "technicality" and assume it is some kind of loophole; a way to escape accountability on a procedural quirk. That framing misses the point entirely.

The Fourth Amendment protection against unlawful searches and seizures is not a technicality. It is one of the foundational rights guaranteed to every person in this country. When law enforcement violates that right — even in a DUI case — the courts are not going to simply look the other way because the violation produced incriminating evidence.

The suppression of unlawfully obtained evidence is the law working exactly as the founders intended. It is the mechanism that keeps police accountable and protects every citizen from government overreach. If evidence obtained through an illegal stop were allowed in court, it would give law enforcement a perverse incentive to skip the legal requirements whenever they wanted to investigate someone.

Put simply: you are not asking to escape the consequences of what you did. You are asking the government to prove its case against you without relying on evidence it should never have had in the first place.

Every Case Is Different

A motion to suppress is not appropriate in every DUI case, and filing one does not guarantee a dismissal. The outcome depends entirely on the specific facts — what the officer observed, what they wrote in their report, what the video shows (if any), and how the judge rules at the suppression hearing.

What it does mean is this: if you have been charged with a DUI, the stop itself is worth examining carefully. Many people charged with DUI never ask whether the stop was legal in the first place. They assume the process was followed correctly and focus only on the breath or blood test results. That can be a costly mistake.

An experienced criminal defense attorney will review the circumstances of your stop as one of the very first things they do — because if the stop was unlawful, everything else may fall with it.

The case examples described above are based on actual matters handled by the Law Office of Sophie C. Bidet. Client identities and identifying details have been omitted to protect confidentiality. Past results do not guarantee a similar outcome in your case. Every case turns on its own facts.