Search Warrant Requirement

The Fourth Amendment to the United States Constitution protects people’s right “to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures.” Police must obtain a search warrant from a judge, although courts have identified exceptions to this rule, such as emergency situations and items plainly visible to police officers. A defendant may ask a court to suppress evidence obtained in violation of the Fourth Amendment, which prevents the state from using it in a criminal trial.

Search Warrant Requirements

The Fourth Amendment itself identifies the criteria for obtaining a lawful search warrant. A police officer, or other official seeking a warrant, must establish probable cause to the satisfaction of a judge, must make an “[o]ath or affirmation” as to the truth of the matters supporting probable cause, and must “particularly describ[e] the place to be searched, and the persons or things to be seized.” A search warrant is invalid if it covers too broad an area or does not identify specific items or persons.

Establishing Probable Cause

The Supreme Court has defined “probable cause” as an officer’s reasonable belief, based on circumstances known to that officer, that a crime has occurred or is about to occur. See Carroll v. United States, 267 U.S. 132, 149 (1925). An officer may establish probable cause with witness statements and other evidence, including hearsay evidence that would not be admissible at trial. An officer’s suspicion or belief, by itself, is not sufficient to establish probable cause. Aguilar v. Texas, 378 U.S. 108, 114-15 (1964).

Exclusionary Rule

The “exclusionary rule” requires courts to suppress evidence obtained through an unlawful search or seizure. See Mapp v. Ohio, 367 U.S. 643 (1961). Any evidence derived from illegally obtained evidence must also be suppressed. This type of evidence is known as “fruit of the poisonous tree.” Silverthorne Lumber Co. v. United States, 251 U.S. 385 (1920; Nardone v. United States, 308 U.S. 338, 341 (1939.

Electronic Searches and Seizures

Computers and the internet present new challenges, since digital evidence might be stored on devices in a suspect’s possession or on the various Internet servers known as the “cloud.” The Supreme Court has ruled that a warrant is required to search the contents of computers, cell phones, and other devices. Cloud storage remains a subject of contention, with different courts reaching different conclusions.

Exceptions to Warrant Requirement

Exigent Circumstances: Courts have allowed warrantless searches in situations where it would be impractical or dangerous to delay a search in order to obtain a warrant. This might include an imminent threat to an officer’s safety, or a reasonable belief that a suspect will dispose of or destroy evidence while police are waiting for a warrant.

Consent to Search: A police officer does not need a warrant to conduct a search if a person with legal authority over the items or premises consents to a search. Another person who also has legal authority over the premises may overrule consent to a search, but the Supreme Court held in Fernandez v. California, 571 U.S. ___ (2014), that the person must be physically present to prevent the search.

Search Incident to Lawful Arrest: Police officers may conduct a limited search of a person when they have placed the person under arrest. The search must be limited to the area of the person’s immediate control and be for the purpose of checking for weapons and evidence. Chimel v. California, 395 U.S. 752 (1969). Police must obtain a warrant, however, to search a person’s cell phone after an arrest. Riley v. California, 571 U.S. ___ (2014).

Automobile Exception: Related to the “lawful arrest” exception, this allows police to search a vehicle without a warrant during the lawful arrest of the driver, but only if they reasonably believe that (1) the person under arrest might still be able to access the vehicle’s passenger compartment, or (2) the vehicle contains evidence relevant to the offense for which they are arresting the person. Arizona v. Gant, 556 U.S. 332 (2009).

“Plain View” and “Open Fields” Exceptions: An officer may seize property that is visible from a location where the officer is lawfully present, provided that the officer has probable cause to believe the property is contraband. Coolidge v. New Hampshire, 403 U.S. 443 (1971). This might include items that are visible in the front seat of a vehicle during a lawful traffic stop. “Open fields,” defined as open areas of a person’s property that are not directly adjacent to his or her residence, are not protected by the Fourth Amendment and may be searched without a warrant. Hester v. United States, 265 U.S. 57 (1924); Oliver v. United States, 466 U.S. 170 (1984).

Terry Stops: The Supreme Court held in Terry v. Ohio, 392 U.S. 1 (1968), that police may “stop and frisk” a person based on reasonable suspicion that the person has been, is, or will soon be involved in criminal activity. “Reasonable suspicion” is a lower standard than “probable cause.” Evidence discovered in the course of what is now known as a Terry stop is admissible, even if police did not have a warrant.

Border Searches: Officials at the United States border, as well as airports and seaports that handle international travel, have broad discretion to conduct searches of individuals, their personal effects, and their vehicles. See United States v. Montoya de Hernandez, 473 U.S. 531 (1985); United States v. Flores-Montano, 541 U.S. 149 (2004).