Colorado Adopts a Four-Factor Reasonableness Test for Delays in Seeking Search Warrants After a Probable-Cause Seizure: People v. Mills (2025 CO 47)

Introduction

In People v. Mills, 2025 CO 47, the Colorado Supreme Court (en banc) resolved a recurring Fourth Amendment question: when police lawfully seize property based on probable cause but do not search immediately, how long can they hold the property before seeking a warrant without rendering the seizure unconstitutional? The Court rejected a rigid “necessity only” approach and, aligning Colorado law with influential federal circuit decisions, adopted a fact-intensive four-factor reasonableness test.

The case arises from a Saturday surveillance of suspected drug activity in Denver, culminating in the seizure and impound of Arthur S. Mills’s vehicle, followed by a three-day delay before a search warrant application was filed. The trial court suppressed the narcotics evidence, concluding the car was held longer than “necessary” to obtain a warrant. On interlocutory appeal under section 16-12-102(2) and C.A.R. 4.1, the Supreme Court reversed, holding the delay reasonable under the newly announced test.

Parties: The People of the State of Colorado (Plaintiff-Appellant) and Arthur S. Mills (Defendant-Appellee). Opinion by Chief Justice Márquez, joined by all Justices.

Summary of the Opinion

Holding: A seizure supported by probable cause that is extended while police seek a search warrant is evaluated under a four-factor balancing test focused on reasonableness—not necessity.
New Rule: Courts weigh (1) the length of the delay, (2) the nature and strength of the individual’s possessory interest, (3) the strength of the government’s justification for the delay, and (4) the government’s diligence in applying for a warrant.
Application: A roughly three-day delay (over a weekend) before seeking a warrant to search Mills’s impounded vehicle was reasonable in the totality of the circumstances. The suppression order is reversed, and the case is remanded.
Constitutional Framework: The Fourth Amendment’s touchstone is reasonableness. The Court treated article II, section 7 of the Colorado Constitution as coextensive here and did not adopt a separate state constitutional standard.

Background, Facts, and Procedural History

During a Saturday covert surveillance of a high-crime area, officers observed what they believed was a drug transaction in a Walgreens lot involving Mills and an unidentified man. After Mills departed without signaling, officers conducted a traffic stop. Mills lacked a driver’s license and proof of insurance for the Range Rover, presented insurance for three other high-end vehicles, used three different phones during the stop, refused to exit, and became combative.

Although officers believed they had probable cause to arrest and to search, they opted against a forcible extraction and consulted off-duty narcotics Detective Kevin Burke. Following Burke’s instruction, officers impounded the vehicle and issued traffic citations. Burke took no action over the weekend. On Monday, he requested a K-9 sniff, but the K-9 unit was off duty; the sniff occurred Tuesday morning, with a positive alert. Burke submitted a warrant application later Tuesday afternoon, and a judge signed it about an hour later. The search revealed methamphetamine, heroin, cocaine, fentanyl, and digital scales. Mills was charged with multiple counts of possession with intent to distribute.

The trial court suppressed the evidence, reasoning the vehicle was held longer than necessary to obtain a warrant and applying a “necessity” benchmark the court attributed to Chambers v. Maroney. The People sought interlocutory review. The Supreme Court reversed.

Analysis

Precedents Cited and Their Influence

Chambers v. Maroney, 399 U.S. 42 (1970): The trial court read Chambers to impose a “necessity” limit on how long police may hold a vehicle pre-warrant. The Supreme Court clarified that Chambers did not adopt a necessity standard for warrant delays. Chambers upheld a warrantless vehicle search based on probable cause, noting no constitutional difference between searching at the scene and seizing-and-holding to present probable cause to a magistrate. It did not address how long police may hold property before seeking a warrant when they choose not to search immediately.
Illinois v. McArthur, 531 U.S. 326 (2001): The Court endorsed a reasonableness analysis for temporary restraints to preserve evidence while police diligently obtain a warrant (there, a two-hour restriction on reentry to a home). McArthur’s references to “no longer than reasonably necessary” and “police diligence” anchor the focus on reasonableness rather than necessity.
United States v. Place, 462 U.S. 696 (1983): Establishes overall balancing—intrusion on possessory interests versus law enforcement interests—in assessing reasonableness of temporary property seizures pending investigation (e.g., K-9 sniff). Place emphasizes duration and the degree of interference with possessory interests.
Segura v. United States, 468 U.S. 796 (1984): Recognizes that a seizure reasonable at inception can become unreasonable due to its duration or other factors.
United States v. Burgard, 675 F.3d 1029 (7th Cir. 2012): A leading circuit decision articulating that length of delay, possessory interest, government justification, and diligence all matter. It cautions against punishing careful investigative work simply because a court can imagine faster alternatives with hindsight.
United States v. Smith, 967 F.3d 198 (2d Cir. 2020): Another leading decision articulating a duty of diligence to seek warrants when property is seized for that purpose. Smith stresses the property’s nature and the extent the individual’s possessory interests are disrupted, and it warns a heavy caseload alone does not justify open-ended delay.
United States v. Laist, 702 F.3d 608 (11th Cir. 2012) and United States v. Mitchell, 565 F.3d 1347 (11th Cir. 2009): Address the significance of the item seized—particularly digital devices—in gauging the weight of possessory interests and the constitutional tolerance for delay.
United States v. Christie, 717 F.3d 1156 (10th Cir. 2013): Reinforces the context-specific nature of reasonableness; other investigative priorities can sometimes justify delay.
United States v. Sullivan, 797 F.3d 623 (9th Cir. 2015) and United States v. Sharpe, 470 U.S. 675 (1985): Confirm that reasonableness does not require the least intrusive or quickest imaginable alternative; police imperfection does not automatically equal unreasonableness.
Colorado authorities on standards of review and Fourth Amendment reasonableness: People v. Thompson, 2021 CO 15 (reasonableness is the Fourth Amendment’s touchstone); People v. Davis, 2019 CO 84 (deference to factual findings); People v. Deaner, 2022 CO 43 (de novo review of legal conclusions); Eddie’s Leaf Spring Shop & Towing LLC v. PUC, 218 P.3d 326 (Colo. 2009), People v. Rodriguez, 945 P.2d 1351 (Colo. 1997), People v. Taylor, 41 P.3d 681 (Colo. 2002) (coextensiveness of state and federal protections in this domain); People v. McKnight, 2019 CO 36 (distinct marijuana-related privacy considerations, not controlling here).

These authorities collectively steer Colorado toward a reasonableness framework that balances competing interests and rejects bright-line or necessity-only limits on the permissible duration of a pre-warrant seizure.

Legal Reasoning

The Court begins with first principles: the Fourth Amendment prohibits unreasonable searches and seizures. When police seize property based on probable cause to preserve evidence while securing a warrant, that seizure may become unconstitutional if the delay in obtaining the warrant is unreasonable. Thus, reasonableness is the touchstone.

To guide trial courts, the Court formally adopts a four-factor balancing test (drawn from Place, Burgard, Smith, and related cases) to assess the constitutionality of the delay between seizure and warrant application:

(1) Length of the delay. There is no bright line. The longer the delay, the more it burdens the individual’s possessory interest, and the stronger the justification and diligence must be.
(2) Nature and strength of the individual’s possessory interest. Courts assess both the type of item (e.g., vehicles versus highly personal digital devices) and the practical importance of the property to the person (e.g., essential transportation, ongoing business use), including whether the interest was diminished or reasserted.
(3) Government’s justification for the delay. Courts examine objective reasons for not seeking a warrant sooner (e.g., safety concerns, investigative complexity, unavailability of specialized resources, competing high-priority duties). A bare heavy caseload is not enough.
(4) Government’s diligence. Police must act with a time-sensitive duty to pursue the warrant, though reasonableness does not demand the earliest possible moment or the least intrusive means. Careful, attentive police work should not be discouraged.

The Court expressly repudiates a strict “necessity” standard in this context. While language in Chambers and McArthur mentions necessity or limited duration, those cases are rooted in a broader reasonableness analysis. The Court emphasizes that the inquiry is context-specific and fact-intensive.

Application to Mills

Length of delay: Roughly three days, largely spanning a weekend. The Court characterizes this as “relatively brief,” especially considering practical constraints recognized in other circuits (e.g., weekends, holidays).
Possessory interest: Although vehicles are valuable and often essential, Mills’s specific interest was attenuated: he had no valid license or insurance for the Range Rover, and he appeared to have access to other vehicles. The record is mixed on whether his counsel sought return the night of the seizure.
Government justification: Officer safety concerns and on-scene impracticalities (Mills’s refusal to exit; absence of available K-9 units). Detective Burke pursued a K-9 sniff before seeking a warrant to strengthen probable cause, reflecting careful rather than dilatory police work.
Diligence: While Detective Burke mistakenly believed the police could hold the vehicle for a week because a warrant can be executed within seven days, the record shows he engaged the K-9 unit promptly on Monday, continued drafting the warrant while awaiting the sniff, obtained the sniff Tuesday morning, and submitted the warrant that afternoon. The Court declines to penalize this sequence simply because a faster alternative was theoretically possible over the weekend.

Weighing these factors, the Court concludes the delay was reasonable; thus, continued seizure pending the Tuesday warrant application did not violate the Fourth Amendment. Because the delay was reasonable, the Court does not reach the good-faith exception.

Impact and Forward-Looking Implications

People v. Mills establishes a binding, practical framework for Colorado courts and law enforcement when property is lawfully seized pending a search warrant. The opinion:

Clarifies that reasonableness, not necessity, governs the length of a pre-warrant seizure.
Adopts a four-factor test that will guide trial courts through a structured, record-based analysis rather than a rigid stopwatch rule.
Signals that short delays spanning weekends with documented investigative steps and resource constraints will often be reasonable, particularly for vehicles.
Warns that indefinite or poorly justified delays, or delays showing lack of diligence, remain constitutionally infirm and risk suppression.
Highlights that the type of property matters. For personal electronic devices (phones, laptops), courts will scrutinize delays more closely because the possessory disruption is generally more significant than with vehicles.
Encourages law enforcement to document investigative choices (e.g., safety concerns; specialized unit availability; steps taken while awaiting resources) to demonstrate diligence and justification for any delay.
Provides defense counsel a clear roadmap to challenge delays by focusing on possessory harms, the absence of concrete investigative steps, and availability of earlier warrant application based on facts known at seizure.

Practically, Mills should reduce suppression litigation rooted in mechanical necessity arguments and shift the inquiry to the quality of police decision-making. It also aligns Colorado with persuasive federal authority (Second, Seventh, Tenth, Eleventh Circuits) and promotes statewide uniformity.

Complex Concepts Simplified

Seizure vs. Search: A “seizure” is taking control of property (e.g., impounding a car). A “search” is examining it for evidence. Police can sometimes seize without a warrant if they have probable cause and need to prevent loss of evidence, but they must then diligently seek a search warrant or the seizure can become unreasonable.
Possessory Interest: This is the individual’s interest in using and controlling their property. The law weighs how much a delay interfered with that interest. For example, taking someone’s only phone for days is more disruptive than holding a suitcase for several hours.
Automobile Exception vs. Seize-Then-Search: Under the automobile exception, police with probable cause may search a car without a warrant. Alternatively, they may seize and hold the car while seeking a warrant. Mills concerns the latter choice and how long police may hold the car pre-warrant.
K-9 Sniff: A dog sniff can corroborate probable cause. In Mills, officers already believed they had probable cause, but pursued a K-9 sniff to reinforce their showing before seeking a warrant. The Court viewed that as careful police work, not undue delay.
Reasonableness, Not Necessity: The Constitution does not require officers to act at the earliest conceivable moment or in the least intrusive manner; it requires that, in context, choices made and time taken are reasonable and diligent.
Diligence: Documented, continuous steps toward obtaining a warrant—requesting specialized units, drafting affidavits, coordinating logistics—demonstrate diligence. Mere inaction, or a vague “heavy caseload,” generally does not.
Coextensive State and Federal Protections: For warrantless searches and seizures, Colorado’s Constitution typically parallels the Fourth Amendment. The Court applied the federal standard here; it did not adopt a broader state rule in this case.

Practical Takeaways

For Law Enforcement:
- Maintain a clear timeline of investigative steps taken between seizure and warrant application.
- Articulate safety considerations and logistical constraints (e.g., unit availability, weekends), and continue working the case (drafting, coordinating) during any waiting periods.
- Do not rely on mistaken “safe harbors” (e.g., confusing warrant execution deadlines with permissible seizure duration). Reasonableness remains case-specific.
- Be mindful that digital devices and items integral to daily life will demand swifter action and stronger justifications for any delay.
For Defense Counsel:
- Develop the record on the client’s possessory harms: essential transportation, sole phone or computer, business needs, and attempts to retrieve the item.
- Scrutinize whether facts supporting probable cause were fully known on day one; if so, argue that extended delay shows lack of diligence.
- Probe government justifications: Are they specific and credible, or merely generalized workload assertions?
For Trial Courts:
- Apply the four-factor test rigorously, making fact-specific findings on each factor.
- Avoid bright-line rules; the constitutionality of a delay turns on the totality of the circumstances.
- Consider both the type of property and any record evidence of the individual’s practical need for it.

Conclusion

People v. Mills is a significant Fourth Amendment decision for Colorado. It abandons a rigid “necessity” lens and installs a nuanced, four-factor reasonableness test to assess delays in seeking a search warrant after a probable-cause seizure. Applying that test, the Court held that a three-day delay—mostly over a weekend—was reasonable where the defendant’s possessory interest was limited, the government’s justifications were concrete (safety and resource availability), and the detective acted diligently by coordinating a K-9 sniff and drafting the warrant promptly thereafter.

The decision promotes careful police work while preserving meaningful constitutional limits: delays must be supported by specific, contextual reasons and accompanied by diligent action. Mills will guide Colorado courts, law enforcement, and litigants toward a more transparent, balanced analysis of pre-warrant seizure durations, with special attention to the nature of the property and the realities of investigation. In that sense, it offers both clarity and flexibility—anchoring future disputes in reasonableness, not rigid necessity.