Criminal charges are the result of investigations. Even those charges that start with an anonymous tip are investigated by police before the district attorney’s or a prosecutor’s office decides to bring charges against a person.
Before obtaining a warrant or arresting someone, police must have probable cause, the requirement that protects a person’s Fourth Amendment right against illegal search and seizure (the arrest). Probable cause exists when the facts and circumstances within the police officer’s (or another law enforcement official’s) knowledge are sufficient enough that a reasonable person would believe that the person arrested or searched was committing or had committed a crime. While police need probable cause to arrest, they need only reasonable suspicion to start an investigation. Consider reasonable suspicion to be a lower form of probable cause.
Both probable cause and reasonable suspicion ask whether a reasonable person in the officer’s position would act on the information. Courts use all evidence available or what is called a “totality of the circumstances” analysis to determine if either probable cause or reasonable suspicion exists.
Keep in mind that the standards for probable cause and reasonable suspicion are much less than what is needed to convict a person of a crime. Probable cause authorizes a more severe intrusion, and therefore, law enforcement must meet a higher standard than reasonable suspicion. Probable cause is a fair probability or a reasonable ground that a crime was committed or is being committed.
While reasonable suspicion requires fewer articulable facts, the officer must still demonstrate that he or she had more than just a subjective belief or hunch. Reasonable suspicion permits the brief stop of a person and may justify limited searches.
Many arrests occur after searches. While there are exceptions, law enforcement officials must usually have a warrant to conduct any search of a person’s home, vehicle or belongings. The establishment of probable cause is crucial to a search warrant because without it, the search violates the Fourth Amendment to U.S. Constitution. Pennsylvania’s Constitution also contains a provision against illegal search and seizure through Article I, Section VIII of that document.