City of Helena v. C. Brown, 403 P.3d 341

At ~2:00 a.m., Officer Petty began a traffic stop near Helena’s walking mall; while occupied he heard a vehicle revving in a nearby parking garage and worried it might exit unsafely.
Officer Cook, responding as backup, was directed by Petty to stop a pickup Petty identified; Cook observed the pickup emitting a large quantity of smoke and stopped it.
The driver, Christopher Brown, admitted revving the engine; the stop developed into a DUI investigation and Brown was arrested.
Brown moved to suppress evidence in municipal court, arguing Officer Cook lacked particularized suspicion; the municipal court denied the motion, finding Cook had suspicion based on excessive smoke and Petty’s directive.
The District Court reversed, concluding the record did not support suspicion of wrongdoing; the State appealed to the Montana Supreme Court.
The Supreme Court reviewed whether particularized suspicion existed (including whether Cook could rely on Petty’s observations) and reversed the District Court, reinstating the municipal court’s denial of suppression.

Issue	Plaintiff's Argument	Defendant's Argument	Held
Whether Officer Cook had particularized suspicion to stop Brown’s truck	The State: Cook had objective facts (excessive smoke + Petty’s report of revving) permitting a stop	Brown: Observations did not show unsafe operation; revving alone (or ambiguous exhaust) is insufficient for suspicion	Court: Yes. Cook had particularized suspicion from his observation of excessive smoke and could rely on Petty’s directive; suppression denial reinstated

State v. Larson, 243 P.3d 1130 (Mont. 2010) (officers’ combined observations supported reasonable suspicion to stop)
Grinde v. State, 813 P.2d 473 (Mont. 1991) (hearing revving after vehicle left sight insufficient for particularized suspicion)
State v. Gouras, 102 P.3d 27 (Mont. 2004) (officer may act on another officer’s directive when that officer had reasonable suspicion)
State v. Crawford, 371 P.3d 381 (Mont. 2016) (focus on objective data; subjective motives inappropriate in assessing stops)
City of Missoula v. Sharp, 358 P.3d 204 (Mont. 2015) (reasonable suspicion depends on totality of circumstances)
State v. Seaman, 124 P.3d 1137 (Mont. 2005) (standard of review for suppression rulings)