Probable Cause vs. Reasonable Suspicion

Instructor: Millicent Kelly

Millicent has been teaching at the university level since 2004. She holds a Bachelor's degree in Criminal Justice and a Master's degree in Human Resources.

Probable cause and reasonable suspicion are two legal terms often used by law enforcement and in police work. This lesson will define these terms and distinguish them from each other by providing examples.

Drunk Driving

A police officer sitting in the parking lot across from a popular bar, notices a car leaving the bar that is swerving back and forth and unable to stay in its lane. After following the car for a few blocks, the officer pulls the car over and asks the driver to exit the vehicle. The officer notices the smell of alcohol on the driver's breath and proceeds to give the driver a series of sobriety tests, which the driver fails. The driver is taken into custody and arrested for driving under the influence. When the case gets to court, the legality of the traffic stop is brought into question.

Reasonable Suspicion

Reasonable suspicion is a commonly used term in law enforcement. It is regarded as being more than thinking a crime has been committed but less than probable cause. It refers to as what a reasonable person, or a normal, average person, would consider suspicious. As with probable cause, reasonable suspicion is subjective to a law enforcement officer's discretion. Once established, it allows a law enforcement officer to hold someone briefly and pat them down.

Let's go back to the case of the drunk driver discussed above. The officer observed a vehicle leaving a bar parking lot and swerving down the street. The facts here are limited, and the officer doesn't quite have probable cause to make a traffic stop. However, he does have reasonable suspicion that the driver of the vehicle is driving under the influence and can, therefore, make the traffic stop. Reasonable suspicion should be easy to establish in court based on the officer's observations.

An Additional Example of Reasonable Suspicion

Let's take a look at another example of reasonable suspicion:

  • A law enforcement officer is patrolling a neighborhood that has seen several in-home invasions recently. At around 12:30 am, he spots two individuals in dark clothing walking down the street. One of them is carrying a crowbar and the other a bolt cutter. The officer knows these are tools commonly used to illegally enter homes, and he stops the two men based upon reasonable suspicion that they may be the home invaders police are looking for.

Probable Cause

The Fourth Amendment of the United States Constitution protects United States' citizens against unlawful detainment and unlawful searches of their property by requiring that law enforcement authorities show probable cause before any arrest, search, or seizure can take place, whether with or without a warrant. Probable cause is established when officers of the law have access to information that indicates there is a general probability that:

  • a person has committed a crime and needs to be arrested
  • a specific location served as a crime scene and needs to be searched
  • a specific location holds evidence of a crime and needs to be searched
  • items or property at a location have been stolen and need to be seized as evidence

There is no legal definition of the term probable cause. Rather, the determination of probable cause is left up to the discretion of trained law enforcement members who believe they have sufficient information to establish probable cause. It generally refers to what a reasonable or average person would consider probable.

Examples of Probable Cause

The following two examples are cases of when a probable cause can be established:

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