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The Ninth Circuit Expands Probable Cause for State Law Enforcement to Arrest, Search, and Seize based on Evidence of a Violation of Federal Law

Authors:  Rebecca Kutlow and George C. Harris

The Norton Law Firm’s litigation practice includes representation of plaintiffs harmed through constitutional violations by government officials. It has represented wrongfully convicted clients in two recent cases, one of which resulted in a $15 million settlement and one in which the defendants’ appeal of the district court’s denial of their qualified immunity defense was recently argued in the Ninth Circuit, with trial to follow if the Ninth Circuit affirms the district court. This blog addresses a recently decided case United States v. Steinman, 130 F.4th 693 (9th Cir. 2025), wherein the Ninth Circuit, as a matter of first impression, held that a state law enforcement officer may make an arrest, search, or seizure without violating the Fourth Amendment where they believe there is evidence of a federal crime, even if the suspected conduct does not violate state criminal law. This significantly expands the scope of probable cause for arrests by state law enforcement agents, and puts individuals at increased risk of lawful search or seizure by state agents. 

Summary of Facts:

In Steinman, a Nevada state trooper pulled over a car that was driving over the speed limit. As the trooper approached the car, he observed an ammunition box on the floor of the vehicle and saw items covered by a blanket in the back seat. The trooper ran a check of Steinman’s criminal history, which showed a “felony with a guilty disposition.” The trooper determined that the combination of the felony and the ammunition box sitting in the car provided “a little” probable cause to search the car. When Steinman refused to consent to a search of the vehicle, the trooper seized the car. 

After the car was towed, the trooper requested and received a warrant to search the vehicle. During the search, officers found weapons, firearms, ammunition, drugs, and drug paraphernalia. Steinman was charged with being a felon in possession of a firearm and with possession of an unregistered firearm. Notably, Steinman was not charged by the state with possession of ammunition because possession of ammunition by a felon is illegal only under federal law, not Nevada state law. 

Steinman moved to suppress the evidence against him, arguing that his Fourth Amendment rights were violated. The district court granted Steinman’s motion to suppress finding that 1) the traffic stop was unreasonably prolonged; and 2) that the “seizure, search, and prolongation could not be justified by Trooper Boyer’s interest in enforcing the federal prohibition of possession of ammunition by a felon because Trooper Boyer was a state law enforcement officer.” 

The government appealed the district court’s decision. One of the key issues on appeal was whether a state law enforcement officer can have probable cause to justify a search or seizure based on a potential violation of federal law. This is an issue that the Ninth Circuit had “never squarely addressed.” The other primary issue in the case was whether the traffic stop was unconstitutionally prolonged. 

The Ninth Circuit’s Decision

First, the Ninth Circuit disagreed with the district court and found that the traffic stop was not unconstitutionally prolonged under the specific facts of the case. Second, the Ninth Circuit found that the trooper had probable cause to seize the car both because there was probable cause to believe that Steinman had violated Nevada law and because there was probable cause to believe the car contained “evidence of a federal crime—namely, that Steinman possessed ammunition as a felon in violation of 18 U.S.C. § 922(g)(1).” 

The Ninth Circuit held that the fact that the potential crime was only illegal under federal law “pose[d] no barrier” to the state officer’s seizure. The court articulated five reasons why this holding was correct:

  1. The court noted that under the Supremacy Clause, “federal law shall be the supreme Law of the Land.” The court explained that where there is no indication to the contrary, “we may assume that states are concerned with apprehension of offenders against laws of the United States” within their borders even if they cannot be prosecuted in the states’ courts. 
  2. The court noted that even though the Fourth Amendment has been incorporated against the states, “it remains a quintessentially federal standard whose protections do not vary from jurisdiction to jurisdiction.” The court explained that this principle, though not determinative, “cast some light on the best path forward” because “if conduct … is not violative of the Fourth Amendment in one state, it is not violative of the Fourth Amendment in another state.” 
  3. The court referenced “the general rule” that “local police are not precluded from enforcing federal statutes.” The court highlighted an exception to that general rule where “state law enforcement officers are affirmatively prohibited by state law from arresting, searching, or seizing based on evidence of a federal offense.” An example of this exception is California Health and Safety Code § 11362.1(c), which legalized the use of marijuana in California and explicitly stated that “no conduct deemed lawful by this section shall constitute the basis for detention, search, or arrest.” The court contrasted this California law with Steinman’s case, because Nevada law does not contain any provision that prohibits “state law enforcement officers from enforcing the federal ban on felons possessing ammunition.” 
  4. The court found support for its holding from the decisions of two other circuit courts:  United States v. Smith, 899 F.2d 116, 118 (1st Cir. 1990) and United States v. Le, 173 F.3d 1258, 1271 (10th Cir. 1999). Both cases concluded that “evidence of federal crimes may be seized by state officers if that evidence is in plain view.” 
  5. The court emphasized that the “suppression of evidence is an extraordinary remedy that carries a substantial cost to society.” The court explained that the “last resort” remedy of suppression was not appropriate in Steinman’s case “simply because the BMW was seized [by state officers] because it contained evidence of a violation of a federal law rather than state law.” 

Key Takeaways:

Steinmanis significant because, as a matter of first impression in the Ninth Circuit, it expanded the scope of probable cause for state law enforcement officers. Although the court distinguishes its holding from situations where state law enforcement officers are affirmatively prohibited by state law from arresting, searching, or seizing based on evidence of a federal offense, the court’s holding will apply in all other situations.  This means that law enforcement officials in states in the Ninth Circuit can now make lawful arrests, searches, and seizures based on evidence of a federal offense, even if that conduct would not be an offense under state law. For example, where there are no express laws against it, state law officials could use federal crimes related to marijuana use, federal immigration status, or possession of ammunition to support their arrests, searches, and seizures. If states want to protect their residents from such law enforcement action, they will need to pass laws that affirmatively prohibit enforcement of actions and conduct that are legal under state law but not federal law.