Reaffirming Particularized Suspicion to Expand Speeding Stops into DUI Investigations: Commentary on State v. Trimble (Mont. 2025)

I. Introduction

The Montana Supreme Court’s memorandum decision in State v. Trimble, 2025 MT 284N, addresses a recurring and practically important question in DUI enforcement: when may an officer lawfully expand a routine traffic stop (here, speeding) into a full-fledged DUI investigation based on limited indicia of possible impairment?

Although issued as a noncitable memorandum opinion under Section I, Paragraph 3(c) of the Court’s Internal Operating Rules, and thus not formal precedent, the decision illustrates how settled Montana law on “particularized suspicion” is applied to a familiar fact pattern: a daytime speeding stop; an odor of alcohol emanating from the vehicle; bloodshot, watery eyes; some mild confusion; and slightly unusual driving behavior that is still technically lawful.

The parties are:

Appellee (Plaintiff): State of Montana
Appellant (Defendant): Isaac James Trimble

The key issue was narrow but significant:

Did Sergeant Amundson have particularized suspicion to expand a lawful speeding stop into a DUI investigation once he approached Trimble’s vehicle?

Trimble argued that the officer acted on an “undeveloped hunch,” lacking sufficient objective indicators of impairment. Both the Gallatin County Justice Court and the Eighteenth Judicial District Court rejected that view, and the Montana Supreme Court affirmed.

This commentary examines the Court’s reasoning, its reliance on prior authority, and the broader implications for DUI litigation and law enforcement practices in Montana, while also clarifying the legal concepts for non-specialists.

II. Summary of the Opinion

The Court, through Justice Shea, upheld the denial of Trimble’s motion to suppress all evidence gathered after he was asked to exit his vehicle.

The procedural path was:

Trimble was stopped for speeding (72 mph in a 60 mph zone) near Big Sky, Montana.
Upon contact, the officer detected an odor of alcohol from the vehicle, observed bloodshot and watery eyes, perceived Trimble as “a little confused and off,” and noted an unusual delay in slowing down for a marked patrol car.
The officer, suspecting DUI, asked Trimble to exit, conducted field sobriety tests (FSTs), obtained further evidence, and ultimately arrested him.
Trimble moved in Justice Court to suppress all evidence obtained after exiting the vehicle, arguing lack of particularized suspicion to expand the stop beyond speeding.
The Justice Court (after hearing testimony and reviewing dashcam video) denied the motion.
Trimble entered a plea agreement to DUI per se (first offense), reserving the right to appeal the suppression ruling.
The District Court, acting as an intermediate appellate court, affirmed.
The Montana Supreme Court, reviewing as if directly from Justice Court, likewise affirmed.

Substantively, the Court held:

The Justice Court’s factual findings were supported by substantial evidence and were not clearly erroneous.
Under the totality of the circumstances, the officer had particularized suspicion of DUI when he expanded the stop to investigate impairment.
The officer was not required to see a “checklist” of all possible signs of impairment; it was enough that he identified specific, articulable facts from which a reasonable inference of DUI could be drawn.

The Court emphasized that this case was controlled by settled law, justifying resolution by nonprecedential memorandum opinion.

III. Detailed Analysis

A. Procedural Posture and Standards of Review

Understanding the layered review structure is crucial to appreciating the Court’s approach.

1. Justice Court as trial court

Trimble’s case originated in the Gallatin County Justice Court, a court of record. That court:

Heard testimony from Sergeant Amundson.
Reviewed the dashcam video of the stop.
Made factual findings about what the officer observed and how Trimble behaved.
Applied the law of particularized suspicion to those facts and denied suppression.

2. District Court as intermediate appellate court

Under State v. Hoover, 2017 MT 236, ¶ 12, 388 Mont. 533, 402 P.3d 1224, the District Court functions as an intermediate appellate court when reviewing a justice court of record:

It is confined to review of the existing record; no new evidence is taken.
It reviews questions of law arising from the justice court’s decision.

Here, the District Court affirmed the Justice Court’s conclusion that the officer had particularized suspicion.

3. Montana Supreme Court’s review

On further appeal, the Supreme Court reviews the lower court rulings as if appealed directly to this Court. Hoover, ¶ 12. This means:

Factual findings (here, by the Justice Court) are reviewed for clear error (State v. Loberg, 2024 MT 188, ¶ 8, 418 Mont. 38, 554 P.3d 698; State v. Harning, 2022 MT 61, ¶ 13).
Legal conclusions (application of law to facts) are reviewed de novo (fresh, with no deference).

A factual finding is “clearly erroneous” only if:

It is not supported by substantial evidence; or
The court misapprehended the effect of the evidence; or
The reviewing court is left with a firm conviction that a mistake has been made. Harning, ¶ 13.

The Court also underscored that it does not “reweigh conflicting evidence” or substitute its judgment for the trial court’s in assessing the evidence. State v. Wetzel, 2005 MT 154, ¶ 11, 327 Mont. 413, 114 P.3d 269.

This deferential factual standard is important: because the Justice Court had both live testimony and video, its evaluation of what the officer actually saw and how Trimble acted carries significant weight on appeal.

B. Constitutional and Statutory Framework

1. Constitutional protections

The decision is grounded in both federal and state constitutional search-and-seizure provisions:

Fourth Amendment, U.S. Constitution: protects against unreasonable searches and seizures.
Article II, Section 11, Montana Constitution: provides parallel (and sometimes broader) protections.

The Court reiterated that a traffic stop is a “seizure” within these provisions. Harning, ¶ 15. Thus, the stop and any expansion of its scope must be reasonable.

2. Investigative stops and particularized suspicion

Montana codifies the standard for investigative stops at § 46-5-401, MCA, which allows a brief investigative stop when an officer has particularized suspicion that the person is or has been engaged in wrongdoing.

Under State v. Wilson, 2018 MT 268, ¶ 25, 393 Mont. 238, 430 P.3d 77, and State v. Stevens, 2019 MT 36, ¶ 12, 394 Mont. 278, 434 P.3d 904, “particularized suspicion” requires:

objective data from which an experienced police officer can make certain inferences and a resulting suspicion that the individual is or has been engaged in wrongdoing.

This is the Montana articulation of what many jurisdictions term “reasonable suspicion.”

3. Duration and scope of traffic stops

Montana law also governs how long a stop may last and how far it may extend in scope.

A stop may not last longer than is necessary to effectuate the purpose of the stop. § 46-5-403, MCA; State v. Schlichenmayer, 2023 MT 79, ¶ 16.
Officers may prolong or broaden a stop only if the investigation remains within the limits created by the facts and the suspicions from which they arose. Wilson, ¶ 25.
If, while investigating the original basis for the stop, the officer gains additional objective data that supports suspicion of other crimes, the officer may investigate those additional crimes. Schlichenmayer, ¶ 16.

In DUI contexts, this means that a routine traffic stop (for speeding, equipment violation, etc.) may lawfully expand into a DUI investigation if the officer develops particularized suspicion of impairment during the encounter. See Hulse v. State of Mont., Dep’t of Just., Motor Vehicle Div., 1998 MT 108, ¶¶ 40–41, 289 Mont. 1, 961 P.2d 75.

4. DUI statutory framework

The case also references Montana’s DUI statutes:

Original charge: DUI, third offense, in violation of § 61-8-1002(1)(a), MCA (impairment-based DUI).
Amended plea: DUI per se, first offense, in violation of § 61-8-1002(1)(b), MCA (chemical concentration–based DUI).

The difference is:

§ 61-8-1002(1)(a) focuses on whether a person is “under the influence” – i.e., whether alcohol/drugs affect the person’s ability to safely operate a vehicle.
§ 61-8-1002(1)(b) focuses on whether the person’s blood alcohol concentration (BAC) meets or exceeds a per se illegal limit (e.g., 0.08).

Although Trimble ultimately pled to a per se offense, the suppression issue turned entirely on whether the officer lawfully expanded the stop in the first place.

C. Particularized Suspicion and Expansion of a Traffic Stop

1. Trimble’s central argument

Trimble contended that Sergeant Amundson did not have particularized suspicion of DUI when he asked Trimble to exit the vehicle and initiated field sobriety testing. Specifically, he argued:

The officer’s observations did not clearly indicate “actual impairment.”
Many common signs of impairment (e.g., slurred speech, obvious balance issues at the window, weaving, etc.) were absent.
The decision to conduct FSTs was an impermissible “undeveloped hunch,” invoking the language of Hoover, ¶ 18 (citing Illinois v. Wardlow, 528 U.S. 119 (2000)), which distinguishes reasonable suspicion from mere hunches.

2. The Court’s counter-framework: specific and articulable facts, not a checklist

The Court emphasized that officers are required to identify specific and articulable facts supporting suspicion, not to satisfy a rigid checklist of standardized indicators of impairment.

Citing State v. Rodriguez, 2011 MT 36, ¶ 18, 359 Mont. 281, 248 P.3d 850, and Brown v. State, 2009 MT 64, ¶ 22, 349 Mont. 408, 203 P.3d 842, the Court reiterated:

[The officer] was not required to satisfy a checklist of factors. He was required to identify specific and articulable facts which, taken together with reasonable inferences from those facts, reasonably warrant the intrusion.

Thus, Montana law:

Rejects the idea of a numerical or mechanical threshold of signs of impairment.
Demands an individualized, fact-based assessment of the encounter.
Allows officers to consider the overall “feel” of the encounter, as long as that “feel” is grounded in objective observations.

3. The objective data in this case

The Justice Court, and in turn the Supreme Court, relied on several specific facts observed before any FSTs were administered:

Odor of alcohol emanating from the vehicle.
Bloodshot, glassy, watery eyes consistent with possible impairment, as per the officer’s training.
Trimble appeared “a little confused and off” during their interaction.
Trimble exhibited an unusual delay in slowing down when speeding past a marked Highway Patrol vehicle, contrary to what an attentive, unimpaired driver would typically do.
Trimble’s responses regarding the source of the alcohol odor were equivocal and somewhat inconsistent (initial “No, sir, ... Well ... No” while nodding affirmatively).

These observations were corroborated through the officer’s testimony and dashcam video, which the Justice Court found credible.

4. Precedents supporting each factor

Crucially, the Court did not treat these observations in the abstract. It linked them to prior Montana cases that have recognized such indicators as objectively relevant to DUI suspicion:

Odor of alcohol + bloodshot/glossy eyes:
- State v. Flynn, 2024 MT 236, ¶¶ 4, 22, 418 Mont. 331, 557 P.3d 934 (odor of alcohol and bloodshot, glossy eyes supporting suspicion).
- Brown, ¶ 23 (odor of alcohol from the vehicle as significant data point).
- Brunette v. State, 2016 MT 128, ¶ 32, 383 Mont. 458, 372 P.3d 476 (red, watery eyes as a factor supporting DUI suspicion).
Confusion or being “off”:
- State v. Nelson, 2004 MT 13, ¶¶ 4, 9, 319 Mont. 250, 84 P.3d 25 (driver appearing confused as an indicator of potential impairment).
Aberrant yet legal driving behavior:
- State v. Brander, 2004 MT 150, ¶¶ 6–7, 321 Mont. 484, 92 P.3d 1173 (unusual but technically lawful driving can still contribute to suspicion).

Accordingly, none of the indicators relied on by the officer were novel or inherently speculative in Montana jurisprudence; each had already been recognized as potentially probative when viewed in context.

5. Totality of the circumstances

The Court explicitly applied the totality-of-the-circumstances standard articulated in Wilson, ¶ 28, and Hoover, ¶ 17:

Determining particularized suspicion is a factual inquiry determined by examining the totality of the circumstances of the stop and considering the quantity, substance, quality, and degree of reliability of information known to the officer.

It is not that any single factor—odor, eye condition, slight confusion, or delayed slowing—was dispositive. Instead:

Each factor contributed some weight.
The combination of factors, together with the officer’s experience, gave rise to reasonable inferences of impairment.
Under that combined view, it was reasonable for the officer to suspect DUI and to expand the investigation.

The Court therefore held that the Justice Court correctly treated these combined observations as “objective data of driving under the influence,” even if no one factor alone clearly proved impairment.

6. Distinguishing between “hunch” and reasonable suspicion

Trimble’s reliance on the “undeveloped hunch” language from Hoover, ¶ 18 (and Wardlow) was unavailing because:

The officer here did not rely solely on a gut feeling; he articulated specific observable facts.

These facts were of the same type that Montana appellate courts have repeatedly deemed relevant in prior DUI-suspicion cases.

As a result, the Court concluded that:

The officer’s suspicion was sufficiently particularized.
The expansion of the stop to a DUI investigation (including ordering Trimble out of the vehicle and administering FSTs) was reasonable and lawful.

D. Role and Influence of Precedents Cited

Although this is a memorandum opinion, it is tightly integrated with a network of established Montana precedents. Those cases shape, and in turn are exemplified by, the Court’s reasoning in Trimble.

1. State v. Hoover, 2017 MT 236

Hoover serves multiple roles:

Procedural: It defines the District Court’s role as an intermediate appellate court reviewing justice courts of record (¶ 12).
Substantive: It discusses particularized suspicion in traffic-stop contexts and warns against reliance on mere “hunches” (¶ 18).

In Trimble, the Court draws on Hoover for both the standard of review and the conceptual framework distinguishing between grounded suspicion and speculation. It signals that, unlike the “undeveloped hunch” condemned in Hoover, the officer in this case provided the necessary articulable facts.

2. State v. Loberg, 2024 MT 188; State v. Harning, 2022 MT 61; State v. Wetzel, 2005 MT 154

These three cases provide the backbone for the Court’s discussion of appellate review:

Loberg, ¶ 8 – outlines the standard of review for suppression rulings (clear error for facts, de novo for law).
Harning, ¶¶ 13, 15 – defines clear error and reaffirms constitutional search-and-seizure protections.
Wetzel, ¶ 11 – underscores that appellate courts do not reweigh evidence or substitute their own view of the facts.

Together, they constrain the Supreme Court to respect the Justice Court’s factual determinations, which proved decisive here.

3. State v. Wilson, 2018 MT 268; State v. Stevens, 2019 MT 36

Wilson and Stevens are central to Montana’s articulation of particularized suspicion:

Wilson, ¶¶ 25, 28 – states that investigative stops require particularized suspicion, and that such suspicion is judged under the totality of the circumstances with attention to the quantity, substance, and reliability of information.
Stevens, ¶ 12 – provides the now-standard definition requiring objective data and reasonable inferences.

In Trimble, these cases provide the doctrinal test into which the officer’s observations were inserted. The Court’s analysis simply applies those principles to the case-specific facts.

4. State v. Schlichenmayer, 2023 MT 79; Hulse v. State, 1998 MT 108

These cases govern when and how a traffic stop can be prolonged or expanded:

Schlichenmayer, ¶ 16 – clarifies that a stop cannot exceed the time necessary for its original purpose unless new, objective data supports investigation of additional crimes.
Hulse, ¶¶ 40–41 – specifically authorizes expansion of a traffic stop into a DUI investigation when there is additional objective data suggesting impairment.

In Trimble, the Court uses these decisions to justify:

The officer’s shift from addressing speeding to investigating DUI.
The requirement that such a shift be grounded in new observations made during the initial stop.

5. Rodriguez and Brown: rejecting a rigid checklist

State v. Rodriguez, 2011 MT 36, ¶ 18, and Brown v. State, 2009 MT 64, ¶ 22, are deployed to counter Trimble’s “missing signs” argument:

They affirm that particularized suspicion requires “specific and articulable facts” plus reasonable inferences; it does not require every textbook sign of impairment.
They reject the notion that officers must check off a predetermined list of symptoms before escalating an investigation.

This is a key doctrinal point: Montana courts will not invalidate a DUI investigation simply because classic markers (like slurred speech or staggering) are absent, if other objective indicators reasonably support suspicion.

6. Flynn, Brunette, Nelson, and Brander: validating specific indicators

These cases each validate particular categories of evidence as potentially supporting DUI suspicion:

State v. Flynn, 2024 MT 236 – odor of alcohol and bloodshot/glossy eyes.
Brunette v. State, 2016 MT 128 – red, watery eyes.
State v. Nelson, 2004 MT 13 – confusion and disorientation.
State v. Brander, 2004 MT 150 – unusual but legally permissible driving patterns.

By citing this line of cases, the Court demonstrates that each category of observation used in Trimble has already been judicially endorsed as relevant, and that the officer’s reliance on them was firmly grounded in prior law.

7. Illinois v. Wardlow, 528 U.S. 119 (2000)

Wardlow is not discussed directly in Trimble, but it is invoked via Hoover, ¶ 18, for the proposition that mere “hunches” are insufficient. By distinguishing the officer’s concrete observations here from an unarticulated hunch, the Court aligns its analysis with Wardlow’s baseline Fourth Amendment standard as well.

E. Impact and Practical Implications

1. Formal legal impact: nonprecedential but illustrative

By express designation under Section I, Paragraph 3(c) of the Montana Supreme Court’s Internal Operating Rules, Trimble:

“Shall not be cited” and “does not serve as precedent.”
Will be listed only in the Court’s quarterly list of noncitable cases in the Pacific Reporter and Montana Reports.

Formally, this means:

Lawyers cannot rely on Trimble as binding or persuasive authority in briefs or arguments (subject to narrow exceptions like law-of-the-case, if applicable).
Lower courts are not legally bound to follow it as precedent.

Substantively, however, the opinion is a clear and up-to-date illustration of how the Court currently applies the established principles of particularized suspicion and totality-of-the-circumstances analysis in a common DUI fact pattern.

2. Practical guidance for law enforcement

For officers, Trimble reinforces several key points:

Document specific observations. The officer’s success in defending the expansion of the stop hinged on his ability to articulate:
- Odor of alcohol from the vehicle.
- Bloodshot, watery eyes.
- Confused or “off” demeanor.
- Unusual delay in responding to a visible patrol car.
- Equivocal answers related to alcohol consumption and odor.
Use training-based inferences. The Court credited the officer’s testimony that certain physical signs are consistent with impairment “according to his training.”
No need for a checklist. Officers need not wait for every classic DUI indicator to appear; a reasonable constellation of signs suffices.
Dashcam evidence matters. The Justice Court’s reliance on dashcam video, and the higher courts’ deference to that factual assessment, show the evidentiary power of video corroboration.

3. Practical implications for defense counsel

For defense attorneys, Trimble illustrates both challenges and strategies:

Challenges:
- Where there is any combination of recognized DUI indicators (odor, eyes, mild confusion, unusual driving), arguing lack of particularized suspicion becomes difficult.
- Deference to trial courts on factual findings (especially when video evidence exists) means suppression appeals often turn on narrow, fact-specific arguments.
Strategies:
- Focus on whether each alleged indicator is genuinely supported by the record (video, audio, timing, officer reports).
- Highlight benign alternative explanations (fatigue, allergies, road conditions, weather) where the record supports them.
- Scrutinize whether the officer’s suspicion arose before or after the actions the defendant seeks to suppress.

4. Systemic impact on DUI litigation

Although not precedential, Trimble reflects and reinforces a broader trend in Montana DUI jurisprudence:

Low threshold for escalation: A relatively modest set of observable indicators can justify transitioning from a routine stop to a DUI investigation.
Emphasis on “totality” over rigid rules: Courts resist bright-line rules for what is “enough” and instead defer to reasonable inferences from the overall situation.
Reliance on officer experience: Courts allow officers to contextualize physical and behavioral signs in light of their DUI training, so long as that context is tied to concrete observations.

Future cases—especially published, precedential ones—are likely to continue this trajectory, with Trimble serving as an informal example of the Court’s current approach to common DUI-stop fact patterns.

IV. Simplifying Key Legal Concepts

To make the decision accessible to non-lawyers, it is worth clarifying some of the recurring legal terms and ideas.

Particularized suspicion

This is Montana’s statutory term, closely akin to “reasonable suspicion.” It means:

The officer must have specific, objective facts (not just a gut feeling).
From those facts, a reasonably trained officer can draw commonsense inferences that the person is involved in wrongdoing.
The suspicion is “particularized” because it is about this specific person in this specific situation, not based on stereotypes or general hunches.

Totality of the circumstances

This means that courts do not isolate each fact and ask whether it alone proves anything. Instead, courts look at:

All the facts together;
The officer’s training and experience;
The context (time of day, location, road conditions, etc.).

A collection of small indicators, none of which would be decisive by itself, can collectively create reasonable suspicion.

Memorandum opinion (noncitable)

Under the Montana Supreme Court’s Internal Operating Rules, some cases are resolved by brief “memorandum opinions” when:

The issues are controlled by settled law; and
There is no need to elaborate or change existing doctrine.

These opinions:

Are not published as precedents;
Generally cannot be cited in future cases; and
Are included only in lists of noncitable cases in the official reports.

Trimble falls in this category, underscoring that it applies existing rules rather than establishing new ones.

Clear error

An appellate standard applied to factual findings. A finding is “clearly erroneous” only if:

There is not enough evidence to support it;
The trial court misunderstood the evidence; or
The appellate court is firmly convinced a mistake was made.

This is a deferential standard; it is not enough that the reviewing court might have weighed the facts differently.

De novo review

An appellate review standard for legal issues. “De novo” means “from the beginning”:

The appellate court gives no deference to the lower court’s legal conclusions.
The court independently applies the law to the established facts.

DUI vs. DUI per se

In Montana:

DUI (impairment-based) – focuses on whether the driver’s ability to safely operate a vehicle is actually impaired by alcohol or drugs.
DUI per se – focuses on chemical test results (like a BAC of 0.08 or higher) regardless of whether there are obvious signs of impairment.

Trimble ultimately pled to DUI per se, first offense, after originally being charged with DUI, third offense, impairment-based.

Expansion of a traffic stop

When an officer pulls someone over for a limited reason (e.g., speeding), the stop is initially justified only to handle that issue (checking license and registration, issuing citation, etc.). The officer may “expand” the stop—ask more questions, conduct FSTs, etc.—only if new observations provide particularized suspicion of other crimes (like DUI).

V. Conclusion

State v. Trimble does not create new law, and by its own terms it does not serve as precedent. But it is a clear, contemporary illustration of how Montana courts currently apply settled principles of particularized suspicion and totality-of-the-circumstances analysis to DUI investigations.

The key takeaways are:

An officer may lawfully expand a speeding stop into a DUI investigation when, during the initial encounter, he observes:
- Odor of alcohol from the vehicle;
- Bloodshot, watery eyes;
- Mild confusion or “off” demeanor; and
- Unusual driving behavior (even if technically legal, such as delayed slowing for a patrol car),
and when those observations are consistent with impairment in light of the officer’s training and experience.
Montana law does not require a rigid checklist of impairment signs; rather, specific and articulable facts, coupled with reasonable inferences, are sufficient.
Trial courts’ factual findings, particularly when supported by video and officer testimony, receive substantial deference on appeal.
Even nonprecedential decisions like Trimble signal to practitioners how the Court views common DUI-stop fact patterns, reinforcing the relatively low but fact-bound threshold for expanding traffic stops where alcohol-related indicators are present.

In the broader legal landscape, Trimble demonstrates continuity rather than change: it confirms that Montana’s framework for evaluating investigative stops remains rooted in objective data, reasonable inferences, and deference to fact-finder determinations, while providing concrete guidance for how that framework plays out in day-to-day DUI enforcement.