Your Rights: Reasonable Suspicion, Probable Cause

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Reasonable suspicion and probable cause are two legal standards that set how much police must know before they stop, search or arrest someone. With reasonable suspicion, an officer may make a brief stop to investigate; it takes more than a hunch but less than probable cause. Probable cause is a reasonable ground for believing someone is guilty. It is more than bare suspicion, though less than the evidence needed to convict, and it is what police need for an arrest or a search warrant.

Neither standard is a blank check. Grounds for a stop do not automatically justify a frisk for weapons, and one person’s arrest does not give police automatic grounds to arrest someone watching it.

What Police Need Before Restricting Your Freedom

The Fourth Amendment protects people, houses, papers and possessions against unreasonable searches and seizures. A seizure is a restriction on a person’s freedom, not just the confiscation of property. The first distinction is between being approached and being compelled to stay.

Officers generally may ask questions, request identification or seek consent to search without suspecting a particular person, provided they do not convey that compliance is required. In Florida v. Bostick, a bus passenger’s freedom of movement was restricted by a factor independent of the police, his being on the bus, so asking whether he felt free to leave was not the right test. The test, the Supreme Court said, is whether a reasonable person would feel free to decline the officers’ requests or end the encounter, taking all the circumstances into account.

Reasonable suspicion requires objective justification beyond a hunch, but considerably less evidence than probable cause. Probable cause concerns practical probabilities and requires more than bare suspicion but less evidence than would justify a conviction. The distinction allows investigation before guilt is established while reserving more intrusive action for stronger grounds.

Reasonable Suspicion: Specific Facts, Limited Intrusion

The standard comes from Terry v. Ohio, in which the Supreme Court held that a brief, investigatory stop is permitted when the officer has a reasonable, articulable suspicion that criminal activity is afoot. The officer must be able to point to specific and articulable facts that, together with rational inferences from them, reasonably justify the particular intrusion. Articulable means the officer can explain the facts behind the suspicion. A confident assertion that something felt wrong does not substitute for that explanation.

A brief investigatory stop based on suspected criminal activity must be justified at its beginning and reasonably related in scope to the circumstances that justified it. The reason for the stop therefore limits what the investigation can become.

A protective frisk, a pat-down for weapons, requires a reasonable belief that the person is armed and dangerous, though the officer need not be absolutely certain a weapon is present. In Terry, the officer patted down the outer clothing of Terry and his two companions and confined the search to what was minimally necessary to learn whether they were armed and to disarm them; he did not conduct a general exploratory search for evidence. A stop does not automatically allow a frisk: suspicion of an offense and concern about a weapon answer different questions.

In United States v. Arvizu, the Supreme Court said observations must be weighed together, not discarded one by one because each has a possible innocent explanation. Several ordinary acts can take on a different meaning in combination.

Presence in an area of expected criminal activity does not, by itself, establish reasonable suspicion about a particular person. Illinois v. Wardlow treats unprovoked flight upon noticing police as a relevant factor in context, while recognizing that flight does not necessarily indicate wrongdoing.

In Florida v. J.L., an anonymous caller’s allegation about a gun provided no predictive information, leaving police without means to test the informant’s knowledge or credibility. The Supreme Court says the later discovery of a gun did not establish that the officers had adequate grounds before the frisk. A search’s success cannot supply the justification missing when it began.

In Navarette v. California, by contrast, the court found a 911 caller’s report that a specific vehicle had run her off the road reliable enough for the officer to credit. She claimed eyewitness knowledge, called apparently soon after the incident and used a 911 system with safeguards against false reports.

Probable Cause: A Fair Probability, Not Proof of Guilt

For an arrest, probable cause exists when trustworthy facts and circumstances known to officers would lead a reasonably cautious person to believe an offense has been or is being committed. The assessment concerns the information available when police act, rather than a verdict reached afterward. The Supreme Court’s Maryland v. Pringle opinion explains that probable cause cannot be reduced to a precise percentage and must be particularized to the person searched or seized.

For a search warrant, Illinois v. Gates directs the issuing judge to decide whether all the circumstances establish a fair probability that illegal goods or evidence of a crime will be found in a particular place. The arrest question concerns a person’s involvement; the search-warrant question concerns what is likely to be found and where. The Fourth Amendment also requires a warrant to particularly describe the place to be searched and the people or things to be seized.

Under the Fourth Amendment, probable cause can support a warrantless arrest in public for a felony, or for a misdemeanor committed in the officer’s presence. That public-arrest rule does not answer the separate question of entering a home or searching digital information.

Real-World Applications

Traffic Stops and Vehicle Searches

In Whren v. United States, people challenging a traffic stop argued that police may be tempted to use common traffic violations as a means of investigating other crimes. The Supreme Court answered that an officer’s ulterior motives do not invalidate police conduct justified by probable cause. The court agreed that the Constitution prohibits selective enforcement based on race, but said the basis for objecting to intentionally discriminatory enforcement is the Equal Protection Clause, not the Fourth Amendment.

Rodriguez v. United States says authority for a traffic detention ends when tasks tied to the traffic violation are, or reasonably should have been, completed. The court has tolerated certain unrelated investigations, such as questioning, when they did not lengthen the roadside detention. Extending a traffic stop to conduct a dog sniff violates the Fourth Amendment when there is no additional reasonable suspicion.

Under United States v. Ross, a warrantless automobile search supported by probable cause is limited by the object sought and the places where there is probable cause to believe it may be found. Probable cause to believe a particular container in a taxi’s trunk holds contraband does not justify searching the entire cab.

Homes and Emergency Aid

Payton v. New York identifies warrantless searches and seizures inside a home as presumptively unreasonable.

For emergency aid, officers may enter without a warrant when there is an objectively reasonable basis to believe an occupant is seriously injured or imminently threatened with such injury. In Case v. Montana, the Supreme Court held that the emergency-aid standard does not require probable cause, a requirement it said is rooted in the criminal context. The justification is the need to help someone facing serious injury, rather than the probability of finding criminal evidence. The court also said the standard for home entries is different from the reasonable suspicion standard that applies to relatively non-invasive street stops.

Can You Be Arrested for Standing Near an Arrest?

Standing nearby, by itself, does not supply probable cause to arrest a bystander. Ybarra v. Illinois involved a customer who happened to be in a public tavern when police carried out a warrant to search it. The Supreme Court said that merely being near others independently suspected of crime does not, without more, give rise to probable cause to search a person; the probable cause must be particular to that person.

In Pringle, the court distinguished that tavern customer from three men in a small car, where the quantity of drugs and cash made it reasonable to infer a common enterprise among them. The difference is evidence connecting people to an offense, rather than their distance from one another.

City of Houston v. Hill recognizes constitutionally protected freedom to verbally oppose or challenge police action and rejects an ordinance permitting arrest for simply annoying or offensive words or conduct. The ordinance’s text prohibited assaulting, striking or in any manner opposing, molesting, abusing or interrupting officers performing their duties, or people summoned to help make an arrest. On June 15, 1987, the Supreme Court affirmed the judgment holding the ordinance facially invalid as substantially overbroad under the First Amendment. Criticism is not automatically interference simply because it makes an officer’s work less comfortable. That protection does not turn every act performed while criticizing police into protected speech.

California Penal Code section 148(a)(1), for example, prohibits willfully resisting, delaying or obstructing an officer in the discharge or attempted discharge of duties. The Ninth Circuit’s opinion in Lemos v. County of Sonoma describes a California trial for resisting, obstructing or delaying an officer: to convict, the jury had to find that the officer was lawfully performing his duties and that the defendant knew, or reasonably should have known, he was an officer doing so. The jury was also told that an officer who is unlawfully arresting or detaining someone, or using unreasonable or excessive force, is not lawfully performing his or her duties. Those were instructions to a jury deciding the case afterward; the American Civil Liberties Union (ACLU) of Rhode Island says police misconduct cannot be challenged on the street and advises people not to physically resist officers.

Physical conduct that blocks an officer from reaching another person can raise an obstruction issue that merely watching does not. California section 148(g) expressly says photographing or recording an officer in public, or from a place where the recorder has a right to be, does not by itself violate section 148(a), establish reasonable suspicion for detention or establish probable cause for arrest. The California example illustrates why both the conduct and the applicable jurisdiction matter; it is not a nationwide definition of obstruction. An arrest for that offense still needs probable cause connecting the bystander’s own conduct to the offense’s requirements.

Phones and Location Records

Riley v. California says police generally may not search digital information on a phone seized from an arrested person without a warrant.

Under Carpenter v. United States, the government generally needs a warrant for historical cell-site location records, which link a phone to cell sites, though case-specific exceptions such as emergency circumstances may apply. Carpenter expressly leaves real-time cell-site information and tower dumps, collections of devices connecting to a particular cell site during an interval, undecided.

Consent, Identification and Questioning in Custody

When a person is not in police custody, Schneckloth v. Bustamonte requires consent to a search to be voluntary, assessed from all the surrounding circumstances. Knowledge of the right to refuse is a factor, but the state need not prove that the person knew consent could be withheld.

The ACLU of Rhode Island recommends clearly stating that consent to a search is not given. Refusing consent does not prevent a search that has an independent lawful basis, such as an automobile search supported by probable cause. The group also says a person has the right to ask whether he or she is under arrest and, if not, to calmly leave. The answer helps separate a request for cooperation from a detention, but an encounter short of arrest is not always one a person may leave: a stop based on reasonable suspicion is also a detention.

Hiibel v. Sixth Judicial District Court of Nevada upholds Nevada’s requirement to disclose a name during a stop based on reasonable suspicion. As interpreted in that decision, the Nevada statute requires a name, not a driver’s license or another identification document. A rule governing a lawful Nevada detention cannot be treated as a universal obligation for every police conversation.

Miranda v. Arizona addresses custodial interrogation, meaning police questioning after someone has been taken into custody or otherwise significantly deprived of freedom of action. Under Miranda, if a person being questioned in custody indicates that he wishes to remain silent, the interrogation must cease; if he asks for an attorney, it must cease until an attorney is present. Under Berghuis v. Thompkins, a suspect must invoke those rights unambiguously. Merely staying silent, or making an ambiguous statement, does not require police to end the interrogation.

When an Unlawful Search Reaches Court

Mapp v. Ohio establishes that evidence obtained through unconstitutional searches or seizures is inadmissible in state court. Exclusion, often called suppression, concerns whether evidence may be used, rather than rewriting what happened during the encounter. But the rule has exceptions.

United States v. Leon permits the use of evidence obtained in objectively reasonable reliance on a search warrant that was later invalidated. The court added that it was not suggesting exclusion is always inappropriate when an officer has obtained a warrant.

Nix v. Williams allows admission when the prosecution proves by a preponderance of the evidence, meaning more likely than not, that lawful means would ultimately or inevitably have discovered the information. That is a claim about a lawful route to the evidence, not an argument that the original intrusion was acceptable.

For people who feel their rights have been violated, the ACLU of Rhode Island recommends writing down everything remembered, including officers’ badge and patrol car numbers, getting contact information for witnesses and filing a written complaint with the agency’s internal affairs division or civilian complaint board. It says anyone injured should photograph the injuries but seek medical attention first. For a specific encounter, seek advice from a lawyer who can assess the facts and the law that applies. A useful account separates what officers knew from what they did next: the facts supporting a stop may not support the frisk, arrest or search that followed.