What’s the Difference Between Probable Cause and Reasonable Suspicion?

Reasonable suspicion and probable cause are two concepts that law enforcement employs when determining whether to detain someone for questioning, search for and seize evidence, or make an arrest.

The standards for reasonable suspicion and probable cause were established by the U.S. Supreme Court, and while these concepts share similarities, they are also distinguished by some key differences. Following, the Denver criminal defense attorneys at Wolf Law discuss when and how reasonable suspicion and probable cause may be applied.

What Is Reasonable Suspicion?

Driver pulled over by police, giving ID to officer
If a police officer witnesses a car narrowly miss other vehicles and drift between lanes as it travels down a street, the officer has grounds for reasonable suspicion to stop the driver.

The parameters for reasonable suspicion were set by the Supreme Court in a 1968 case. The court ruled that law enforcement officers can briefly detain a person if—based on the officer’s relevant training and experience—there is reasonable suspicion that a person has committed a crime, is currently engaged in criminal activity, or plans to commit a crime.

The standard for reasonable suspicion is more specific than a hunch but broader than probable cause. Although reasonable suspicion is somewhat subjective, it must still be informed by the facts and circumstances at hand.

Perhaps the best way to understand reasonable suspicion is through a real-world example:

A police officer witnesses a man stagger to his car and enter the vehicle. The officer watches as the vehicle lurches from its parking space, narrowly missing another car, and drifts between lanes as it travels down the street.

Based on direct observations backed by law enforcement training and first-hand experience, the officer has reasonable suspicion that the man may be driving under the influence of alcohol or other drugs and can make a traffic stop. But the officer cannot search the man’s vehicle or arrest the man until the officer demonstrates probable cause.

What Is Probable Cause?

Probable cause is required to issue warrants to search or seize property, or to make an arrest. The Fourth Amendment to the U.S. Constitution affirms that citizens have the right to freedom from unreasonable searches and seizures, and that a search warrant cannot be issued without probable cause.

Police Officer Making Traffic Stop
If, upon interacting with a stopped driver, a police officer smells alcohol, sees the driver’s eyes are bloodshot, and notices that the driver’s speech is slurred, the officer has probable cause to make an arrest.

Probable cause must also exist to make an arrest, or to search and seize property without a warrant. The Fourth Amendment does not define probable cause, but the Supreme Court established parameters in a 1949 ruling: “Probable cause exists where the facts and circumstances within the officers’ knowledge, and of which they have reasonably trustworthy information, are sufficient in themselves to warrant a belief by a man of reasonable caution that a crime is being committed.”

Because most DUI arrests—and many other arrests that result in criminal charges—are made without warrants, it’s critical that both law enforcement officers and citizens understand the basic elements of reasonable suspicion and probable cause.

In the example above, the police officer saw a man stumble to his car, merge dangerously into traffic, and swerve recklessly while driving; these observations provide grounds to apply reasonable suspicion and stop the driver. As the example story continues, the officer observes whether there may be probable cause for arrest:

The police officer signals for the driver to pull over, and the man complies. Upon interacting with the driver, the officer smells alcohol on the man’s breath, sees that the man’s eyes are bloodshot, and notices that the man’s speech is slurred and his responses to questions are unintelligible.

The officer now has probable cause to make an arrest for suspected DUI. In this scenario, the officer may try to further establish probable cause by asking the driver to consent to a preliminary breath test. If the test indicates a blood-alcohol content of .08 percent or greater, the officer has probable cause for an arrest.

It’s important to note that Colorado drivers are not required to take a preliminary breath test. Furthermore, the results of a preliminary breath test cannot be used in court, except in a hearing to determine whether an officer had probable cause to make the arrest.

Proving Probable Cause

Law enforcement officers must be able to clearly articulate their use of probable cause in a sworn statement called an Affidavit of Probable Cause. If probable cause isn’t supported by facts and evidence, improper police action could result in reduced charges or criminal charges being dismissed.

The legality of probable cause must be determined before or after an arrest, search or seizure. This is accomplished at a probable cause hearing, either before law enforcement takes action or during a preliminary hearing, which typically follows the arraignment of an arrested suspect.

During the hearing, the defendant can argue that probable cause didn’t exist in the circumstances leading up to arrest. If probable cause can’t be supported by the prosecution, it’s likely the case will be dropped.

If you’re facing a DUI or other criminal charges in Colorado, you need a knowledgeable criminal defense lawyer on your side. Call Denver’s Wolf Law today at 720-479-8574 or contact us online for your free consultation.

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