United States v. Cunningham, 630 F. App'x 873

On March 21, 2014, Denver police stopped a car driven by Monique Ulloa after observing she left a motel parking lot without signaling; William Cunningham was a front-seat passenger.
Officers searched the vehicle following the stop and found a firearm; Cunningham admitted possession and was indicted under 18 U.S.C. § 922(g)(1) for being a felon in possession.
Cunningham moved to suppress the firearm and his statements, arguing the stop was not justified because Colorado law did not require signaling when turning from a private parking lot onto a public road (a mistake of law by officers).
The district court denied the motion after crediting officer testimony that Ulloa did not signal and concluding the Colorado statute required signaling in these circumstances; Cunningham pleaded guilty conditionally to preserve the suppression issue on appeal.
On appeal the court reviewed reasonableness de novo and applied Heien v. North Carolina, holding an officer’s reasonable mistake of law can support reasonable suspicion for a stop.
The Tenth Circuit affirmed, concluding the officers’ interpretation of Colorado signaling law was objectively reasonable given statutory ambiguity, analogous Colorado authority, and divided trial-court practice.

Issue	Plaintiff's Argument	Defendant's Argument	Held
Whether the stop was justified at inception because a failure to signal occurred when turning from a private parking lot onto a public road	Cunningham: No traffic violation occurred; officers erred as a matter of law in concluding a signal was required	Government: Officers reasonably (and the district court correctly) interpreted Colo. Rev. Stat. § 42-4-903 to require a signal in these circumstances; alternatively, stop justified by totality of circumstances	Held: Stop justified — under Heien, officers’ reasonable mistake of law was objectively reasonable; suppression denied
Whether an officer’s reasonable mistake of law can justify reasonable suspicion for a traffic stop	Cunningham: Officer’s legal mistake cannot justify stop (relying on earlier Tenth Circuit precedent)	Government: After Heien, reasonable mistake of law can support reasonable suspicion	Held: Heien controls — a reasonable mistake of law may support reasonable suspicion if objectively reasonable

Illinois v. Rodriguez, 497 U.S. 177 (officer’s reasonable factual mistakes may be excused for Fourth Amendment purposes)
Brigham City v. Stuart, 547 U.S. 398 (reasonableness is the Fourth Amendment touchstone for seizures)
Heien v. North Carolina, 574 U.S. 54 (2014) (a reasonable mistake of law can give rise to the reasonable suspicion necessary to uphold a seizure)
United States v. McHugh, 639 F.3d 1250 (10th Cir. 2011) (standard of review for suppression rulings)
United States v. Botero-Ospina, 71 F.3d 783 (10th Cir. 1995) (traffic stops analyzed as investigative detentions requiring reasonable suspicion)
United States v. Nicholson, 721 F.3d 1236 (10th Cir. 2013) (pre-Heien Tenth Circuit holding that mistakes of law by officers are not excused)
United States v. Tibbetts, 396 F.3d 1132 (10th Cir. 2005) (same)
Sigrist v. Love, 510 P.2d 456 (Colo. App. 1973) (Colorado appellate case applying traffic law where conduct occurred on public street despite collision on private property)