A note before the cases: this page is general legal information about published court decisions, not legal advice and not a training manual. Constitutional rulings set a floor; state law and department policy are often stricter, and courts refine these doctrines constantly. Anyone relying on a case professionally should verify it is still good law with a citator. For background on how court decisions bind, see what case law is.
Terry v. Ohio: Stop and Frisk
Terry v. Ohio, 392 U.S. 1 (1968), created the modern investigative stop. A Cleveland detective watched two men repeatedly walk past a store window, peer in, and confer — conduct he read as casing the store for a robbery. He stopped them and patted down their outer clothing, finding a revolver.
The Supreme Court held that an officer may briefly detain a person based on reasonable suspicion — specific, articulable facts suggesting criminal activity is afoot — a standard lower than the probable cause needed for arrest. And if the officer reasonably suspects the person is armed and dangerous, the officer may conduct a limited pat-down of outer clothing for weapons. Two limits are built into the rule: the suspicion must rest on articulable facts rather than a hunch, and the frisk is a protective weapons search, not a general search for evidence. Nearly every “Terry stop” question since 1968 has been about those two limits.
Graham v. Connor: The Use-of-Force Standard
Graham v. Connor, 490 U.S. 386 (1989), supplies the constitutional test for claims that police used excessive force during a stop or arrest. Dethorne Graham, a diabetic having an insulin reaction, was forcibly detained by officers who mistook his behavior for intoxication and was injured in the process.
The Court held that such claims are analyzed under the Fourth Amendment’s objective reasonableness standard — not under substantive due process and not by asking whether the officer acted in good faith. Reasonableness is judged from the perspective of a reasonable officer on the scene, allowing for split-second judgments, rather than with hindsight. The opinion lists factors now known as the Graham factors: the severity of the crime at issue, whether the suspect posed an immediate threat to officers or others, and whether the suspect was actively resisting or attempting to flee. Every police use-of-force case in federal court starts here.
Tennessee v. Garner: Deadly Force
Tennessee v. Garner, 471 U.S. 1 (1985), ended the old common-law rule that officers could use deadly force to stop any fleeing felon. Memphis police shot 15-year-old Edward Garner as he fled an empty house burglary, unarmed, climbing a fence.
The Court held that deadly force to prevent a suspect’s escape is a Fourth Amendment seizure and is unconstitutional unless the officer has probable cause to believe the suspect poses a significant threat of death or serious physical injury to the officer or others. Where feasible, a warning should precede its use. Garner and Graham together frame nearly all deadly-force litigation: Garner supplies the rule for fleeing suspects, Graham the general reasonableness lens.
Pennsylvania v. Mimms: Traffic Stops
Pennsylvania v. Mimms, 434 U.S. 106 (1977), answered a small question with large consequences: once a vehicle is lawfully stopped, may the officer order the driver out? The Court said yes — the additional intrusion on the driver is minimal, and it is outweighed by officer safety concerns around roadside stops. No extra suspicion is required. Twenty years later, Maryland v. Wilson, 519 U.S. 408 (1997), extended the same rule to passengers. Together they are among the most-cited cases in day-to-day traffic enforcement, and they pair with the other traffic-stop decisions in our guide to landmark Supreme Court cases.
Search and Seizure Essentials for Officers
Beyond the big four, a compact set of Fourth Amendment decisions does most of the work in suppression hearings:
- The exclusionary rule. Mapp v. Ohio, 367 U.S. 643 (1961), applied it to the states: evidence from an unconstitutional search is generally inadmissible.
- What counts as a search. Katz v. United States, 389 U.S. 347 (1967), tied the Fourth Amendment to reasonable expectations of privacy — “the Fourth Amendment protects people, not places.”
- Pretext stops. Whren v. United States, 517 U.S. 806 (1996): a stop is valid if probable cause of a traffic violation exists, whatever the officer’s underlying motive.
- Stop duration. Rodriguez v. United States, 575 U.S. 348 (2015): a stop may not be extended beyond the time needed for its mission — even a few minutes for a dog sniff — without independent reasonable suspicion.
- Vehicle searches after arrest. Arizona v. Gant, 556 U.S. 332 (2009), narrowed search-incident-to-arrest for vehicles to cases where the arrestee could access the car or it likely contains evidence of the offense of arrest.
- Digital evidence. Riley v. California, 573 U.S. 373 (2014), requires a warrant to search a phone’s data, and Carpenter v. United States (2018) requires one for extended historical cell-site location records.
A Police Case Law Cheat Sheet
One line per case — the shorthand version officers and students actually memorize:
| Case | Rule in one line |
|---|---|
| Terry v. Ohio (1968) | Brief investigative stop on reasonable suspicion; frisk for weapons if suspicion the person is armed and dangerous. |
| Pennsylvania v. Mimms (1977) | Officer may order the driver out of a lawfully stopped vehicle. |
| Tennessee v. Garner (1985) | Deadly force against a fleeing suspect only with probable cause of a significant threat of death or serious injury. |
| Graham v. Connor (1989) | Use of force judged by Fourth Amendment 'objective reasonableness' from the on-scene officer's perspective. |
| Maryland v. Wilson (1997) | Officer may order passengers out of a lawfully stopped vehicle, extending Mimms. |
| Whren v. United States (1996) | A traffic stop is valid if there is probable cause of a traffic violation, regardless of the officer's subjective motive. |
| Arizona v. Gant (2009) | Vehicle search incident to arrest only if the arrestee could reach the car or it likely holds evidence of the offense of arrest. |
| Riley v. California (2014) | Searching a cell phone's data generally requires a warrant, even incident to arrest. |
| Rodriguez v. United States (2015) | A traffic stop may not be prolonged beyond its mission (e.g., for a dog sniff) without independent reasonable suspicion. |
A cheat sheet is a memory aid, not authority. Doctrines like qualified immunity, state constitutional law, and department policy all modify how these rules play out, and any of these cases can be refined by the next term’s decisions — which is exactly why researchers check a citator before relying on one.