A motion to suppress is a written request asking the judge to exclude evidence because the police obtained it unlawfully. In a Montana DUI case it usually challenges the traffic stop or the arrest, and if it is granted, the evidence that flowed from that step "is not admissible at trial" (MCA § 46-13-302(3)). It is decided by the judge before trial, never by the jury. This page is part of our Montana DUI Guide. Our page on DUI defenses surveys what these motions look for. This one explains how the motion itself works.
What a Motion to Suppress Is
Montana has two suppression statutes. The first covers physical and observational evidence: a defendant "aggrieved by an unlawful search and seizure may move the court to suppress as evidence anything obtained by the unlawful search and seizure" (MCA § 46-13-302(1)). The second covers statements: a defendant may move to suppress "any confession or admission" on the ground that it was involuntary (MCA § 46-13-301(1)).
Neither statute asks whether you were impaired. A suppression hearing is about what the officer knew and did at each step, measured against the legal standard for that step. That is why a motion can succeed even when a test result is over the limit, and why it can fail even when the rest of the State's case is thin.
Common Grounds in a DUI Case
| Step challenged | The question | MCA |
|---|---|---|
| The stop | Did the officer observe circumstances creating a particularized suspicion of an offense? | § 46-5-401(1) |
| The length of the stop | Did it last longer than necessary to carry out its purpose? | § 46-5-403 |
| The arrest | Was there probable cause to believe you were committing or had committed an offense? | § 46-6-311(1) |
| A search | Was a search of you, your vehicle, or your blood lawful? | § 46-13-302(1) |
| A statement | Was a confession or admission involuntary? | § 46-13-301(1) |
The stop. An officer may stop a vehicle "that is observed in circumstances that create a particularized suspicion that the person or occupant of the vehicle has committed, is committing, or is about to commit an offense" (MCA § 46-5-401(1)). The motion tests whether the facts the officer actually had meet that standard. See challenging the traffic stop and reasons police can stop you.
The length of the stop.A stop "may not last longer than is necessary to effectuate the purpose of the stop" (MCA § 46-5-403). A stop for a broken taillight that turns into a DUI investigation has to be justified by what the officer learned along the way.
The arrest. A warrantless arrest requires probable cause to believe the person is committing or has committed an offense (MCA § 46-6-311(1)). In a DUI case the probable cause usually rests on the officer's observations and the field sobriety tests, so how those tests were given can matter here as well as at trial.
When and How It Is Filed
A suppression issue is one that can be decided without a trial, so it "must be raised at or before the omnibus hearing" unless there is good cause (MCA § 46-13-101(1)). Failing to raise it at the time set by the court is a waiver, subject to relief for cause shown (MCA § 46-13-101(2), (3)). Our page on the omnibus hearing explains that deadline.
The motion must be in writing, supported by a statement of the relevant facts, and must state its grounds and the relief sought with particularity (MCA § 46-13-101(4)). A motion to suppress a statement must likewise be written and state facts showing why the statement was involuntary (MCA § 46-13-301(1)). This is why discovery comes first. The facts in the motion come from the reports and the video.
The Suppression Hearing
If the motion "states facts that, if true, would show that the evidence should be suppressed," the court must hear its merits, at the omnibus hearing or at a later date (MCA § 46-13-302(2)). A motion that only states a conclusion may be denied without a hearing.
At the hearing, the arresting officer typically testifies and is cross-examined, and the recording of the stop is played. The judge decides both the facts and the law. For a motion to suppress a statement, the statute places the burden on the prosecution to prove by a preponderance of the evidence that the statement was voluntary (MCA § 46-13-301(2)). The search-and-seizure statute does not spell out a burden in its text. That allocation comes from case law and depends on the kind of police action at issue.
The court's final ruling must state its findings of fact and conclusions of law, in writing or on the record (MCA § 46-13-104(3)), and a pretrial motion must generally be decided before trial (MCA § 46-13-104(1)).
If the Motion Is Granted
The suppressed evidence cannot be used at trial. What happens next depends on what was suppressed:
- If the stop itself was unlawful, the officer's observations, the field tests, and the breath or blood result usually all came from it. The prosecutor may have nothing left and may dismiss.
- If only one piece is suppressed, such as a statement, the case can continue on the rest.
- The State may appeal. Montana law allows the prosecution to appeal an order whose substantive effect is suppressing evidence, or suppressing a confession or admission (MCA § 46-20-103(2)(e), (f)).
No one can promise that a granted motion ends a case. It changes what the State can prove, and the prosecutor decides what to do with what remains.
If the Motion Is Denied
A denial means the evidence comes in. It does not decide guilt, and the same facts can still be argued to the jury as reasons to doubt the officer's conclusions. You then have the usual choices: trial, or a negotiated resolution.
If you believe the ruling was wrong, there are two ways to get it reviewed. You can go to trial and, if convicted, appeal. Or, "with the approval of the court and the consent of the prosecutor," you can enter a plea of guilty or no contest while reserving the right to appeal the ruling on a specified pretrial motion. If you win that appeal, you must be allowed to withdraw the plea (MCA § 46-12-204(3)). This matters in the lower courts because an ordinary guilty plea there waives the right to a new trial in district court (MCA § 46-17-203(2)(a)). See appealing to district court.
Suppression and the License Case
A suppression ruling is made in the criminal case. A refusal suspension is challenged separately, by a petition in district court limited to whether the officer had a basis for requesting the test and whether you refused (MCA § 61-8-1017(4)). The questions overlap but the cases are different, with different deadlines. See test refusal and implied consent.
This page explains Montana procedure in general as of the 2025 Montana Code Annotated. Whether a motion has merit depends on the facts of the stop and arrest. It is not legal advice about your specific case.