Policing Case Law Database

The Fourth Amendment permits brief investigative stops when officers have reasonable, articulable suspicion of criminal activity — a standard lower than probable cause but more than a hunch.

Probable cause requires a fair probability — more than reasonable suspicion but less than certainty — that evidence of a crime will be found or that a person has committed an offense.

Traffic stops are Fourth Amendment seizures. Officers may stop vehicles for any observed traffic violation; the stop's duration must be limited to its mission unless additional reasonable suspicion develops.

Vehicles have a reduced expectation of privacy. The automobile exception permits warrantless searches when there is probable cause to believe a vehicle contains evidence of a crime.

Officers may conduct a limited pat-down for weapons when they have reasonable suspicion that a person is armed and dangerous. The frisk is limited to the outer clothing and may not become a general search.

Dog sniffs are not Fourth Amendment searches when conducted in public spaces, but may not be used to extend a traffic stop without independent reasonable suspicion.

Consent is a recognized exception to the warrant requirement. Consent must be voluntary — not the product of duress or coercion — but officers are not required to advise persons of their right to refuse.

The home receives the highest Fourth Amendment protection. Warrantless entry is presumptively unreasonable, with narrow exceptions for exigent circumstances, hot pursuit, and emergency aid.

Officers may search a person incident to a lawful arrest without a warrant. The scope of the search is limited to the person and the area within their immediate control.

Officers may seize evidence in plain view without a warrant when they are lawfully present, the item is in plain view, and its incriminating nature is immediately apparent.

The Fourth Amendment protects persons, not places. A search occurs when the government violates a subjective expectation of privacy that society recognizes as reasonable.

Warrants must be supported by probable cause, issued by a neutral magistrate, and describe with particularity the place to be searched and items to be seized.

Officers executing a warrant must generally knock and announce their presence before entering. Suppression is not the automatic remedy for knock-and-announce violations.

Inventory searches of impounded vehicles are administrative — not investigative — and are valid without a warrant or probable cause when conducted pursuant to standardized procedures.

Sobriety and border checkpoints are permissible without individualized suspicion. Checkpoints designed primarily for general crime control are unconstitutional.

Miranda warnings are required before custodial interrogation. The Fifth Amendment privilege against self-incrimination must be invoked — silence alone is not an invocation.

The Sixth Amendment right to counsel attaches at the initiation of formal criminal proceedings — not at arrest. It is offense-specific and prohibits deliberate elicitation of statements without counsel present.

Eyewitness identification procedures must not be unnecessarily suggestive. Modern research has significantly advanced understanding of eyewitness memory reliability.

Use of force by law enforcement is governed by the Fourth Amendment's objective reasonableness standard. Courts evaluate force from the perspective of a reasonable officer on the scene.

The prosecution must disclose all material exculpatory and impeachment evidence to the defense. Investigators have independent obligations to preserve and disclose evidence.

Section 1983 provides a civil remedy for constitutional violations by government actors. Officers may be entitled to qualified immunity unless they violated clearly established law.

The First Amendment protects speech, assembly, and the right to record police in public. Retaliatory arrests and viewpoint-based enforcement are unconstitutional.

DNA collection from arrestees is constitutionally permissible. Developing areas include investigative genetic genealogy, abandoned DNA, and CODIS database use.