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Distinguishing Reasonable Suspicion And Probable Cause For A Stop

If a law enforcement officer is unable to explain how he or she reasonably came to believe that an individual might be committing a crime, might have committed a crime, or might be about to commit a crime, the law forbids this officer to stop such individual. The concept of “probable cause,” for which there is no formal legal definition, prevents the police and other agents of the government from acting arbitrarily and capriciously in detaining, searching, and arresting individuals.

The Fourth Amendment of the U.S. Constitution reads as follows:

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 seized.

The Fourth Amendment is an important check on arbitrary, intrusive, and oppressive government conduct by protecting people against unreasonable searches and seizures. The Supreme Court initially interpreted this to mean that probable cause must be the basis for any reasonable arrest, search, or seizure.

Probable cause is established when police officers have reliable information indicating that:

  • a person has committed a crime
  • a specific location was a crime scene and needs to be searched
  • a specific location contains evidence of a crime and needs to be searched
  • items or property at a specific location are stolen and must be seized as evidence

Since the landmark decision of Terry v. Ohio in 1968, a “reasonable suspicion” may serve as the basis for stopping an individual, such as for a DUI traffic stop. In Terry, the Supreme Court ruled that the Fourth Amendment’s prohibition on unreasonable searches and seizures is not violated when a police officer stops a suspect on the street and frisks him or her without probable cause to arrest, if the police officer has a reasonable suspicion that the person has committed, is committing, or is about to commit a crime and has a reasonable belief that the person “may be armed and presently dangerous.” Thus, for the last 50+ years, every traffic stop, even a brief detainment, by the police legally considered a “seizure” must have been supported by either probable cause or reasonable suspicion.

Thus, the distinction between probable cause and reasonable suspicion is that the former is based on specific evidence of a crime, whereas the latter is more speculative. Probable cause is the logical belief, fully supported by the facts and the circumstances, that a crime was, is being, or will be committed. Reasonable suspicion is stronger than a “hunch” or guess but weaker than probable cause. It is cited as the basis to justify further investigation into possible criminal activity.

In sum, police generally need only “reasonable suspicion” to justify a DUI traffic stop, but “probable cause” to justify a DUI arrest. Motorists in California who drive under the influence of alcohol or drugs may be charged under California Vehicle Code § 23152(a) VC (driving while under the influence of alcohol), violating California Vehicle Code § 23152(b) VC (driving with a BAC of .08 or higher), and California Vehicle Code § 23152(f) VC (driving under the influence of drugs).

John Patrick Dolan has handled everything from traffic tickets to death penalty murder cases. Mr. Dolan has represented California motorists charged with DUI for over 40 years. He is a recognized California State Bar Certified Specialist in Criminal Law and a true courtroom veteran of DUI cases. Call the Dolan Law Offices today at (760) 775-3739 or find out more online here.

Distinguishing Reasonable Suspicion And Probable Cause For A Stop