The probable cause requirement comes from the Fourth Amendment of the U.S. Constitution, which states that:
"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 searched."
As seen in those words, in order for a court to issue a warrant -- for someone's arrest, or to search or seize property -- there must be "probable cause."
Police must also have probable cause to arrest without a warrant, and in many cases to search or seize property without a warrant.
Prosecutors must also have probable cause to charge a defendant with a crime.
Warrants and Probable Cause
Typically, to obtain a warrant, an officer will sign an affidavit stating the facts as to why probable cause exists to arrest someone, conduct a search or seize property. Judges issue warrants if they agree that probable cause exists.
There are many instances where warrants are not required to arrest or search, such as arrests for felonies witnessed in public by an officer. Here is more information on when warrants are not required.
If a warrantless arrest occurs, probable cause must still be shown after the fact, and will be required in order to prosecute a defendant.
Probable Cause for Arrest
Probable cause for arrest exists when facts and circumstances within the police officer's knowledge would lead a reasonable person to believe that the suspect has committed, is committing, or is about to commit a crime. Probable cause must come from specific facts and circumstances, rather than simply from the officer's hunch or suspicion.
"Detentions" short of arrest do not require probable cause. Such temporary detentions require only "reasonable suspicion." This includes car stops, pedestrian stops and detention of occupants while officers execute a search warrant. "Reasonable suspicion" means specific facts which would lead a reasonable person to believe criminal activity was at hand and further investigation was required.
Detentions can ripen into arrests, and the point where that happens is not always clear. Often, police state that they are arresting a person, place him/her in physical restraints, or take other action crossing the line into arrest. These police actions may trigger the constitutional requirement of probable cause.
Someone arrested or charged without probable cause may seek redress through a civil lawsuit for false arrest or malicious prosecution.
Probable Cause to Search
Probable cause to search exists when facts and circumstances known to the officer provide the basis for a reasonable person to believe that a crime was committed at the place to be searched, or that evidence of a crime exists at the location.
Search warrants must specify the place to be searched, as well as items to be seized.
There are many instances where a search warrant is not required. Common situations in which police are allowed to search without a warrant include:
- when they have consent from the person in charge of the premises (although who that person is can be a tricky legal question);
- when conducting certain searches connected to a lawful arrest; and
- in emergency situations which threaten public safety or the loss of evidence.
Police also do not need a warrant to search or seize contraband "in plain site" when the officer has a right to be present.
Questions often arise over the extent to which police may search vehicles. Here are some commonly asked questions and answers about vehicle searches.
Probable Cause to Seize Property
Probable cause to seize property exists when facts and circumstances known to the officer would lead a reasonable person to believe that the item is contraband, is stolen, or constitutes evidence of a crime.
When a search warrant is in play, police generally must search only for the items described in the warrant. However, any contraband or evidence of other crimes they come across may, for the most part, be seized as well.
Should evidence prove to have resulted from an illegal search, it becomes subject to the "exclusionary rule" and cannot be used against the defendant in court. After hearing arguments from the prosecuting and defense attorneys, the judge decides whether evidence should be excluded.
Probable cause refers to the amount and quality of information required to arrest someone, to search or seize private property in many cases, or to charge someone with a crime. Probable cause to arrest, search, or seize property exists when facts and circumstances known to the police officer would lead a reasonable person to believe:
- that the person to be arrested has committed a crime;
- that the place to be searched was the scene of a crime;
- that the place to be searched contains evidence of a crime; and/or
- that property to be seized is contraband, stolen, or constitutes evidence of a crime.