Odor of Marijuana as Probable Cause for Arrest: Sixth Circuit’s New Fourth Amendment Rule in United States v. Santiago

Introduction

United States v. Edwin Santiago (6th Cir. 2025) addresses a frequently encountered but under-litigated question in Fourth Amendment jurisprudence: whether the odor of marijuana, when localized to a particular individual, supplies not only reasonable suspicion for a brief investigatory stop (“Terry stop”) but also probable cause for a full custodial arrest under 18 U.S.C. § 922(g)(1). The case arises from an encounter on September 21, 2021, when plainclothes detectives of the Metropolitan Nashville Police Department detected a strong smell of marijuana emanating from a car driven by Mr. Santiago, observed a handgun on his waistband, detained and arrested him without a warrant, and ultimately convicted him of being a felon in possession of a firearm. Santiago challenged the constitutionality of the stop, arrest, and ensuing search; the District Court denied his suppression motion; and the Sixth Circuit affirmed. This decision cements a new circuit-wide precedent on the Fourth Amendment standards for drug‐odor stops and arrests.

Summary of the Judgment

The Sixth Circuit unanimously held:

The smell of marijuana, localized to a single occupant exiting a vehicle, provided reasonable suspicion under Terry v. Ohio to detain Santiago.
The same odor, viewed through the lens of an objectively reasonable officer trained to recognize marijuana, supplied probable cause to arrest him for marijuana possession—thus validating the warrantless arrest.
Because the arrest was lawful, the subsequent search incident to arrest (yielding Santiago’s identification and revealing his felon status) was constitutional, and the District Court properly denied the suppression motion.
The within‐Guidelines sentence of 56 months’ imprisonment was presumptively reasonable; the court did not abuse its discretion in weighing the § 3553(a) factors.
Pro se supplemental claims (Speedy Trial, Bail Reform Act, Due Process) were not considered, as Santiago was represented by counsel on appeal.

Analysis

Precedents Cited

Terry v. Ohio (392 U.S. 1, 1968): Established the “stop and frisk” framework requiring reasonable suspicion for brief investigative detentions.
Navarette v. California (572 U.S. 393, 2014): Defined “particularized and objective basis” for suspecting criminal activity.
United States v. Foster (376 F.3d 577, 6th Cir. 2004): Held that odor of contraband can supply reasonable suspicion.
United States v. McCallister (39 F.4th 368, 6th Cir. 2022): Confirmed that the smell of marijuana alone can justify a Terry stop.
Arizona v. Gant (556 U.S. 332, 2009): Recognized the constitutionality of searches incident to arrest.
District of Columbia v. Wesby (583 U.S. 48, 2018): Emphasized that officers need not rule out innocent explanations to establish probable cause.
United States v. Brooks (987 F.3d 593, 6th Cir. 2021): Collected Sixth Circuit cases treating marijuana odor as probable cause to search vehicles.
Sister‐Circuit Authorities:
- Humphries (4th Cir. 2004), Perdoma (8th Cir. 2010), Paige (7th Cir. 2017), Outlaw (3d Cir. 2025): Each held that localized odor of marijuana supplies probable cause to arrest for drug possession.
Atwater v. City of Lago Vista (532 U.S. 318, 2001): Confirmed that officers may arrest for minor offenses so long as probable cause exists.
Riley v. California (573 U.S. 373, 2014): Discussed scope of search incident to arrest, here applied to an arrestee’s wallet.

Legal Reasoning

The Sixth Circuit’s reasoning unfolds in two steps:

Reasonable Suspicion for a Terry Stop: Detectives Tidwell and Miller, trained to recognize the odor of marijuana, testified credibly that they smelled it on Santiago’s car and person. Tennessee law prohibits possession of marijuana. Under Terry and its progeny, that localized odor alone justified a brief investigative detention to confirm or dispel the suspicion.
Probable Cause for Warrantless Arrest: The court held that the quantum of evidence needed to support an arrest parallels that for a search: an objectively reasonable officer must have a “substantial chance” that a crime has occurred. Given the unmistakable marijuana odor emanating solely from Santiago, the officers had probable cause to believe he possessed an illegal substance in their presence. This decision aligns Sixth Circuit vehicle‐search cases (Brooks, Gill) and sister circuits (Humphries, Paige, etc.) in recognizing odor as sufficient for arrest.

The court also rejected Santiago’s argument that he might have been smelling hemp (a legal substance). Citing Wesby, it held that officers need not disprove every innocent explanation when establishing probable cause.

Impact

United States v. Santiago now stands as binding Sixth Circuit authority that:

A localized odor of marijuana supplies both reasonable suspicion for a stop and probable cause for a warrantless arrest.
Warrantless arrests supported by such probable cause validate subsequent searches incident to arrest, including retrieval of identification and discovery of felon status.

This ruling:

Provides law enforcement clear guidance: officers trained in odor detection may rely on that sense to arrest for drug possession without fear of suppression.
Influences future Fourth Amendment challenges in the Sixth Circuit, narrowing the scope for suppression motions based on drug odors.
May invite legislative or administrative responses to clarify training standards for officers in odor identification.
Encourages other circuits to adopt or reaffirm parallel rules, fostering national uniformity on drug‐odor cases.

Complex Concepts Simplified

Terry Stop: A brief, on‐the‐spot detention of a suspect by police based on “reasonable suspicion” of criminal activity—less than probable cause but more than a mere hunch.
Reasonable Suspicion vs. Probable Cause:
- Reasonable Suspicion: A lower threshold allowing short stops (Terry stops).
- Probable Cause: A higher threshold requiring an objectively reasonable belief that a crime has been committed, permitting full custodial arrests and related searches.
Localization of Odor: To arrest based on smell, officers must be able to point to the individual (or vehicle) from which the odor comes; generalized smells in the air are not enough.
Search Incident to Arrest: A lawful arrest authorizes a contemporaneous, warrantless search of the suspect’s person and immediate possessions to protect officer safety and preserve evidence.
Hemp vs. Marijuana Issue: Even if hemp and marijuana smell alike, officers need not eliminate every possible innocent explanation once they have probable cause—they are not required to perform a lab test on the spot.

Conclusion

United States v. Santiago solidifies a clear Fourth Amendment rule in the Sixth Circuit: when an officer trained to recognize the odor of marijuana detects that odor emanating specifically from an individual’s person or vehicle, that alone furnishes both reasonable suspicion for a Terry stop and probable cause for a warrantless arrest. This decision harmonizes prior vehicle‐search odor cases with arrests, reinforces law‐enforcement’s ability to act on sensory cues, and affirms the constitutional validity of searches incident to such lawful arrests. Courts, practitioners, and police agencies should now treat the localized smell of marijuana as a robust basis for arrest and consequent search, subject to the safeguards of objective‐reasonableness review.