The Fourth Amendment to the U.S. Constitution protects people from unreasonable searches and seizures. It goes on to specify that warrants for searches and seizures may only be issued by a court upon a showing of probable cause. The seizure of a person, as occurs during an arrest, is a Fourth Amendment event requiring probable cause. It was left to the Supreme Court and other federal and state courts to clarify the circumstances under which police may arrest a person without first obtaining a warrant.
Meaning of probable cause
Arrest warrants and warrantless arrests must be based upon probable cause according to the Fourth Amendment, but the Constitution does not offer a definition by which courts and police can be guided. Instead, the Supreme Court has been left with the task of giving practical meaning to the concept of probable cause.
Probable cause is, according to the Supreme Court, a concept based upon probabilities that exist based upon the facts and circumstances of each case. As a general rule, probable cause exists when the facts and circumstances known to police are such as to justify a belief in the mind of a reasonable person that a crime is being, or has been, committed by the individual who is about to be arrested.
The concept of probable cause relies quite heavily on the way in which a police officer perceives or interprets the facts and circumstances existing at a particular time and in a specific place. For an arrest to be in compliance with the Fourth Amendment, it must be more likely than not that the individual taken into custody committed the crime for which he or she is charged.
Probable cause arrests without a warrant
Rarely do police find themselves in situations in which there is time to prepare an arrest warrant and go to a judge to have it signed. Situations typically unfold so quickly that an officer observing a person engaging in criminal conduct must take immediate action to prevent harm or injury from occurring.
Whether or not a police officer had probable cause to justify the making of an arrest is an issue that arises later when the arrest is challenged by a defense attorney on behalf of the person charged with committing the crime. At the hearing to determine if probable cause existed to make the arrest, prosecutors will use the testimony of the arresting officer to establish probable cause.
A police officer must be able to clearly verbalize at a hearing the facts and circumstances that existed at the time of the arrest upon which probable cause was based. If a judge disagrees with the officer's assessment, the arrest and any evidence derived from it could be ruled being an unlawful violation of the Constitution.
Arrest warrants may avoid issues with probable cause
An arrest warrant is an order signed by a judge authorizing the police to arrest the person identified in it. A judge must be convinced by sworn affidavits establishing probable cause that the person to be arrested committed a crime. Police are not forced to make on-the-spot decisions about probable cause as they must do when making an arrest without a warrant.