Probable Cause

Imagine walking home late at night and seeing a suspicious person wearing dark clothes, looking into a car window with a flashlight, and carrying a crowbar. There have been multiple reports of vehicle break-ins in the area. Would you A) assume they are just locked out of their car or B) assume they were about to break into the car to steal? Now imagine the same scenario in the shoes of a police officer. The fact the person looks suspicious, carries a blunt object, and is in an area where break-ins are common would be probable cause for an officer to detain them.

Probable Cause Probable Cause

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Table of contents

    This article focuses on the use of probable cause. Along with the definition of probable cause, we will look at how law enforcement uses probable cause during arrests, affidavits, and hearings. We will look at a case example involving probable cause and differentiate probable cause from reasonable suspicion.

    Definition of Probable Cause

    Probable cause is the legal grounds on which a law enforcement officer can conduct a search, seize property, or arrest. Probable cause is the reasonable belief by a law enforcement officer that an individual is committing a crime, has committed a crime, or will commit a crime and is based solely on facts.

    There are four types of evidence that can establish probable cause:

    Type of evidenceExample
    Observational evidenceThings an officer sees, hears, or smells at a possible crime scene.
    Circumstantial evidenceA set of facts that, when put together, suggests a crime was committed. Circumstantial evidence is different from direct evidence and needs to be supplemented by another type of evidence.
    Officer expertiseOfficers skilled in certain aspects of law enforcement may be able to read a scene and determine whether a crime has occurred.
    Evidence from informationThis includes information gathered from police radio calls, witnesses, or confidential informants.

    The Supreme Court has stated that the concept depends on the context and is very imprecise. The court has often opted for a more flexible stance on probable cause in cases with more serious charges.

    Probable Cause Evidence from Information StudySmarterEvidence from information is one of the ways law enforcement can establish probable cause, Diplomatic Security Services, Wikimedia Commons.

    Fourth Amendment Protections

    The Fourth Amendment of the US Constitution protects individuals from searches and seizures by government officials deemed unreasonable under the law.

    Home: The searches and seizures at an individual's home are considered unreasonable without a warrant. However, there are times a warrantless search is lawful:

    • the officer gets consent to search the home;
    • a lawful arrest of the individual has been made in the immediate area;
    • the officer has probable cause to search the area; or
    • the items in question are in plain view.

    Person: An officer may briefly stop a suspicious individual and ask them questions to relieve their suspicions if the officer observes conduct that makes them reasonably believe that a crime will occur or has occurred.

    Schools: A warrant isn't needed before searching a student under a school's care and authority. The search must be reasonable under all circumstances of law.

    Cars: An officer has probable cause to stop a vehicle if:

    • they believe that a car has evidence of criminal activity. They are authorized to search any area of the car evidence can be found.
    • they have reasonable suspicion that a traffic violation or crime has occurred. An officer can pat down the occupants of a car during a lawful traffic stop and have a narcotics detection dog walk around the exterior of the car without reasonable suspicion.
    • law enforcement has a special concern, they are authorized to make highway stops without reasonable suspicion (i.e. routine searches at border stops, sobriety checkpoints to combat drunk driving, and stops to ask motorists about a recent crime that happened on that highway).

    Probable Cause Officers are authorized to stop cars on the highway Stop StudySmarterOfficers can stop a vehicle if they have probable cause a traffic violation or a crime has occurred, Rusty Clark, CC-BY-SA-2.0, Wikimedia Commons.

    Probable Cause Affidavit

    A probable cause affidavit is written by the arresting officer and given to a judge to review. The affidavit summarizes the evidence and the circumstances leading to the arrest; it also contains witness accounts or information from police informants. A probable cause affidavit is written when an officer makes an arrest without a signed warrant from a judge. Cases of warrantless arrests usually occur when officers see someone breaking the law and arrest them at the scene.

    In determining whether there was probable cause for a search, seizure, or arrest, the court must find that under the same circumstances, a mentally competent individual would think a crime was being committed. This procedure is done to make sure police aren't arresting people without reason.

    Arrest on Probable Cause

    When an officer announces that they are placing an individual under arrest and restrains them, they must have probable cause to believe that person committed a crime. Generally, the amount of evidence needed to establish probable cause is more than a suspicion that a crime was committed but less information than needed to prove guilt beyond a reasonable doubt.

    If an officer arrests someone without probable cause, the individual may file a civil lawsuit. Usually, the individual will state they were falsely arrested or prosecuted maliciously. The court will not proceed with the lawsuit if the officer was simply mistaken.

    Probable Cause Hearing

    A probable cause hearing is a preliminary hearing that takes place after charges have been filed against an individual. The court hears witness and officer testimony to determine the likelihood the defendant committed the crime. If the court finds there is probable cause, the case moves forward to trial.

    A probable cause hearing can also refer to a court proceeding that determines whether an officer had a valid reason to arrest an individual. This hearing determines whether law enforcement can continue to hold a defendant who hasn't posted bail or hasn't been released on their own recognizance. This type of hearing occurs in conjunction with the individual's arraignment or first appearance before the judge.

    Example of Probable Cause

    A well-known Supreme Court case involving probable cause is Terry v. Ohio (1968). In this case, a detective watched two men walk along the same route in alternate directions, pause at the same store window, and then continue on their routes. This happened twenty-four times during his observation. At the end of their routes, the two men spoke with each other and during one conference a third man joined them briefly before quickly taking off. Using observational evidence, the detective came to the conclusion that the men were planning to rob the store.

    The detective followed the two men and watched as they met up with the third man a few blocks away. The detective went up to the men and announced himself as a law enforcement official. After hearing the men mumble something, the detective completed pat-downs of the three men. Two of the men were carrying handguns. Ultimately, the three men were arrested.

    The courts noted that the detective had probable cause to stop and frisk the three men because they were acting suspiciously. The detective also had the right to pat down the men for his own protection as he had reasonable suspicion to believe they were armed. The Supreme Court dismissed the appeal of the case because there was no constitutional question involved.

    Probable Cause vs. Reasonable Suspicion

    Reasonable suspicion is used in the various contexts of criminal law involving search and seizure. It's a legal standard that requires a law enforcement officer have an objective, articulable reason for suspecting an individual is involved in criminal activity. Essentially, it's the step before probable cause. Officers can only briefly detain an individual based on reasonable suspicion. Reasonable suspicion can be thought of as a justifiable hunch whereas probable cause is an evidence-based belief of criminal activity.

    Probable cause requires stronger evidence than reasonable suspicion. At the point of probable cause, it is obvious a crime has been committed. Additionally, aside from an officer, any reasonable person looking at the circumstances would suspect the individual of being involved in criminal activity.

    Probable Cause - Key takeaways

    • Probable cause is the legal grounds on which a law enforcement officer can conduct a search, seizure, or arrest.
    • Reasonable suspicion requires an officer to have an objective reason for believing someone has committed or will commit a crime.
    • For probable cause, it is obvious to an officer or to any reasonable person that a crime has been committed and the individual may have been a part of it.
    • If an officer arrests someone without a warrant they will have to write a probable cause affidavit, submit it to a judge, and attend a hearing to determine whether the arrest was legitimate.
    Frequently Asked Questions about Probable Cause

    What is probable cause?

    Probable cause is the legal grounds on which a law enforcement officer can conduct a search, seizure of property, or arrest.

    What is a probable cause hearing? 

    A probable cause hearing determines the likelihood a defendant committed the crimes they are charged with or determines whether an officer's arrest was lawful.

    When is a probable cause hearing necessary? 

    A probable cause hearing is necessary when the court needs to determine whether there is enough evidence to charge the individual with the crime or when an officer performs a warrantless arrest. 

    How is a search warrant related to probable cause? 

    In order to obtain a search warrant signed by a judge, an officer must show probable cause that an individual may have committed a crime. 

    What is the difference between probable cause and reasonable suspicion? 

    Reasonable suspicion is the step before probable cause. An officer has an objective reason for suspecting an individual is involved in criminal activity. An officer can only briefly detain an individual in order to question them about their suspicions.


    Probable cause can lead to the search and seizure of evidence, and the arrest of an individual. Probable cause is based on facts and evidence that even a normal person would look at and determine criminal activity had taken place.

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