What is probable cause?

One of the most frequently used phrases in criminal law is “probable cause.” In Massachusetts, probable cause is necessary to arrest someone, conduct a search without a warrant, detain a person arrested on suspicion of having committed a crime or to obtain a search warrant. The rule applies to both felonies and misdemeanors.

While the definition of the term may vary slightly from state to state, all definitions can be traced to the use of the term in the Fourth Amendment to the United States Constitution, which protects the people from unreasonable searches and seizures of their property. To prove that the search or seizure is reasonable, the Fourth Amendment states, the police must typically have a warrant supported by probable cause.

In this context, probable cause means the belief of a prudent person based upon known facts. For example, probable cause for an arrest exists when facts and circumstances known to the police officer would lead a reasonable person to believe that the suspect has committed, is committing or is about to commit a crime. An officer’s hunch or suspicion unsupported by facts is not sufficient to establish probable cause for issuance of an arrest warrant. Similar requirements apply to facts stated in an affidavit submitted in support of an application for a search or arrest warrant.

The application of the probable cause rule is similar in other circumstances. A search warrant must be supported by an officer’s affirmation that, based upon objective facts, the officer believes that evidence of criminal conduct will be found in the place that is the subject of a search warrant.

Appellate courts are often asked to review a lower court’s determination of probable cause in connection with issuance of a search warrant, a search made without a warrant or the arrest of a suspect. If the lower court’s determination is ruled erroneous, the evidence will be excluded and a conviction based on that evidence may be reversed. If the source of critical evidence is in doubt under the probable cause standard, a capable criminal defense attorney may be able to keep it out of a trial and thereby prevent an improper guilty verdict.

Source: FindLaw, “Probable Cause,” accessed on December 23, 2017