The Fourth Amendment and Probable Cause

The Fourth Amendment of the U.S. Constitution protects citizens from unreasonable searches and seizures and secures a fundamental right to privacy.

It states:

“The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized.”

Central to this amendment is the notion of an "expectation of privacy." Numerous U.S. Supreme Court decisions have refined this idea and dictated:

• How police can gather evidence

• How that evidence can be used in a criminal trial

The court's decisions strive to strike a balance between constitutional rights and law enforcement's capacity to investigate crimes. The legal system manages this by mandating probable cause.

What is Probable Cause?

Probable cause is a fundamental concept in Fourth Amendment jurisprudence. It serves as the threshold for law enforcement to obtain warrants, conduct searches, and make arrests.

Police and judges use probable cause to determine if there is enough reason to believe that:

• A person has committed a crime

• Evidence of a crime is present in a specific location

• There are facts that would make a reasonable person think it’s a crime has occurred or that evidence will be found

A lack of probable cause will render a warrantless arrest invalid, and any evidence resulting from that arrest will be suppressed.

The probable cause requirement ensures a balance between an individual's right to privacy and the government's interest in maintaining public safety and order.

This standard is less stringent than required for a conviction ("beyond a reasonable doubt") but requires more than mere suspicion or hunches.

How is Probable Cause Established?

Probable cause is established through facts and evidence. Police officers gather information through observations, witness statements, or other reliable sources.

Say an officer sees someone breaking into a car. That observation provides probable cause to arrest the person. Similarly, say officers receive a credible tip that a house contains illegal drugs. Officers see people entering and leaving the house at odd hours. This might give them probable cause to get a search warrant.

Is Probable Cause the Same as Reasonable Suspicion?

No, probable cause and reasonable suspicion are not equivalent. Reasonable suspicion is indeed a lesser standard than probable cause. It implies that an officer has sufficient reason to suspect someone might be engaged in criminal activity based on particular facts or circumstances.

Reasonable suspicion allows an officer to stop and briefly question or frisk a person. Probable cause, on the other hand, is a stronger belief based on more concrete evidence. It is required for arrests or obtaining search warrants.

For example, think of a traffic stop. Law enforcement officers must reasonably suspect a traffic violation or criminal activity to comply with the Fourth Amendment. The stop should be brief and limited to addressing the suspected violation. Prolonged detentions or searches require additional justification, such as probable cause.

What Happens if Police Perform a Search Without Probable Cause?

Mapp v. Ohio (1961) addressed the admissibility of evidence obtained through unconstitutional searches and seizures. Police forcibly entered Dollree Mapp's home without a proper warrant. They were searching for a suspect and illegal betting equipment. The evidence found during this search led to her conviction under Ohio law. Mapp argued that the search violated her Fourth Amendment rights.

In an earlier case, the Supreme Court held that evidence obtained without a warrant or probable cause cannot be used in court proceedings. This is known as the exclusionary rule. However, for decades, the rule did not apply to state courts.

The Court's ruling in Mapp v. Ohio extended the application of the exclusionary rule. The rule now applies to state courts through the due process clause of the Fourteenth Amendment.

Landmark Supreme Court Cases on Probable Cause

Several important Supreme Court cases have shaped the interpretation of the Fourth Amendment. The cases discussed below-defined privacy expectations and requirements for probable cause.

Aguilar v. Texas (1964)

In this case, officers received a tip from an unnamed informant that narcotics were being kept in the Aguilar residence. Based on this tip, the police officers submitted an affidavit to obtain a search warrant.The affidavit lacked details regarding the informant and the method by which they obtained their information, yet a warrant was still issued.

Officers found illegal drugs during the search of Aguilar's home. This led to his arrest and conviction for drug possession.

The question on appeal was whether the affidavit used to obtain the search warrant provided sufficient evidence of probable cause under the Fourth Amendment. The Court held that it did not.

The Supreme Court established a two-prong test. To determine whether an affidavit provides enough evidence to support a finding of probable cause, a judge must consider:

• Basis of the knowledge: The affidavit must state the underlying circumstances of the informant's claims.

• Veracity: The affidavit must address the informant’s credibility or the reliability of the information.

In Aguilar's case, the affidavit failed to meet both prongs. It did not provide any details on how the informant obtained the information, nor did it establish the informant's reliability or credibility. Consequently, the search warrant was issued lacking sufficient probable cause, thereby violating the Fourth Amendment.

United States v. Ventresca (1965)

Federal agents conducted surveillance on a residence suspected of being used for the illegal distillation of alcohol. They observed several signs indicating illegal activity, including:

• An unusual amount of traffic at odd hours

• The smell of fermenting mash

• The presence of equipment typically used for distillation

Based on these observations, the agents obtained a search warrant. The search uncovered evidence of illegal distillation, leading to Ventresca’s arrest and conviction.

The issue in this case was whether the affidavit supporting the search warrant established probable cause under the Fourth Amendment. The Supreme Court held that it did because it included detailed descriptions of the agents' observations over an extended period.

The Court reasoned that affidavits for search warrants should be interpreted in a commonsense and realistic manner, not subjected to overly technical scrutiny.

Probable cause does not require proof beyond a reasonable doubt. Only a reasonable ground for belief of guilt based on the totality of circumstances described in the affidavit.

The detailed observations provided a reasonable basis for believing illegal activity occurred at Ventresca’s residence. Therefore, the affidavit met the probable cause requirement of the Fourth Amendment.

Terry v. Ohio and Reasonable Suspicion

Terry v. Ohio expanded the scope of permissible police conduct under the Fourth Amendment.

In this case, Detective Martin McFadden observed two men acting suspiciously near a store. McFadden suspected the men of "casing" the store for a potential robbery. After observing them for some time, McFadden approached the men, identified himself as a police officer, and asked for their names. When the men mumbled in response, McFadden conducted a quick search or "frisk" of the men. During the frisk, McFadden found a pistol on John Terry and another weapon on Richard Chilton. Both were charged with carrying concealed weapons.

The Supreme Court had to decide whether the Fourth Amendment permits a police officer to stop and frisk a person based on reasonable suspicion that the person may be armed and involved in criminal activity.

The Court held that the Fourth Amendment does allow a police officer to stop someone and perform a pat-down, but only if the officer has a reasonable suspicion that the person may be armed and involved in criminal activity.

The Supreme Court acknowledged that a "stop and frisk" is a search and seizure within the meaning of the Fourth Amendment. However, the Court also recognized the need for police officers to protect themselves and others from potential harm. The Court ruled that the search was conducted on reasonable grounds because it was limited in scope and designed to ensure the officer's safety. This limited search is often referred to as a "Terry stop.”

The Court established that for a stop and frisk to be valid under the Fourth Amendment, the police officer must have a reasonable suspicion based on specific and articulable facts, not just a hunch, that the person is involved in criminal activity and may be armed.

The "reasonable suspicion" standard is a lower threshold than probable cause. This ruling provided law enforcement with a practical tool to investigate suspicious behavior without a warrant or probable cause. The decision acknowledged the need for procedural flexibility to ensure officer safety. However, it still provides a measure of constitutional protection against arbitrary intrusions.

Illinois v. Gates (1983) and the Totality of Circumstances Test

In Illinois v. Gates, the Supreme Court refined the concept of probable cause by introducing the "totality of the circumstances" test. This case involved an anonymous tip that Lance and Sue Gates were involved in drug trafficking. The police corroborated the details of the tip through their own investigation, leading to the issuance of a search warrant.

The Court abandoned the rigid two-pronged test established in Aguilar v. Texas (discussed above) and Spinelli v. United States (1969). The old test required a detailed demonstration of the informant’s reliability and the basis of their knowledge.

Instead, the Court adopted a more flexible approach. It allowed magistrates to make a practical, common-sense decision based on all the circumstances outlined in the affidavit, including the veracity and basis of knowledge of persons supplying hearsay information.

The "totality of the circumstances" test considers various factors in their entirety rather than evaluating them in isolation. This approach recognizes that even if individual pieces of evidence may not establish probable cause on their own, their collective weight can suffice. This decision significantly impacted law enforcement by enhancing the ability to act on credible tips and intelligence.

Florida v. J.L. (2000) and Anonymity in Police Tips

Florida v. J.L. addressed the issue of anonymous tips and their sufficiency in establishing probable cause or reasonable suspicion. In this case, an anonymous caller reported that a young Black male standing at a particular bus stop and wearing a plaid shirt was carrying a gun. Acting on this tip, police officers located J.L. and frisked him, discovering a firearm. J.L. was charged with carrying a concealed weapon without a license.

The Supreme Court held that the anonymous tip did not provide enough reliability to justify the stop and frisk. The Court emphasized that an anonymous tip, without more, lacked the necessary indicia of reliability because it did not provide predictive information that the police could independently corroborate.

The ruling underscored the importance of corroborating anonymous tips with additional evidence or observation before acting on them, thus safeguarding against arbitrary and unjustified searches and seizures.

This decision reaffirmed the principle that probable cause and reasonable suspicion must be based on reliable and specific information. It also highlighted the need for law enforcement to conduct thorough evaluations of the credibility and detail of tips before they can infringe on an individual's Fourth Amendment rights.

The Fourth Amendment in Modern Policing

Modern policing requires adherence to the Fourth Amendment's warrant requirements, with specific exceptions. Law enforcement officers must typically obtain a warrant before conducting searches, but exceptions exist for exigent circumstances, such as emergencies or situations where evidence might be destroyed.

The general rule is that searches and seizures are unreasonable unless conducted with a warrant. However, several well-defined exceptions allow law enforcement officers to act without a warrant under certain circumstances:

• Exigent circumstances: When there is an immediate need to prevent physical harm, the destruction of evidence, or the escape of a suspect, officers may conduct a warrantless search or seizure.

• Search incident to arrest: After a lawful arrest, officers may search the person and the immediate area for weapons or evidence. This exception ensures officer safety and prevents the loss of evidence.

• Automobile exception: Given the mobile nature of vehicles, officers can search a vehicle without a warrant if they have probable cause to believe it contains evidence of a crime. The rationale is that obtaining a warrant might not be feasible before the vehicle can be moved.

• Plain view doctrine: If officers are lawfully present at a location and observe contraband or evidence in plain view, they can seize it without a warrant. This requires that the initial entry or intrusion be lawful and that the incriminating nature of the item be immediately apparent.

• Consent: No warrant is required if an individual voluntarily consents to a search. Consent must be freely and intelligently given without coercion or duress.

• Good faith: The good faith exception allows evidence obtained in violation of the Fourth Amendment to be used in court if law enforcement officers acted with the belief that they were following legal procedures.

These exceptions balance effective law enforcement with the protection of individual rights.