Reasonable suspicion & probable cause: What's the difference?

In our post last week, we discussed the types of circumstances under which police can initiate a traffic stop. In order for the stop to be considered valid, the officer must have a “reasonable suspicion” that criminal activity may have taken place, often drunk driving.

Most Americans outside the criminal justice system are familiar with the term “probable cause.” While reasonable suspicion and probable cause are similar concepts, they should not be used interchangeably. Reasonable suspicion may justify a traffic stop followed by limited investigation. But a DUI arrest generally cannot be made until the officer has established probable cause, which is a higher standard.

In the context of a DUI-related traffic stop, reasonable suspicion could be based on erratic driving. This could turn out to be nothing, and that’s why the standard is pretty low. In order to establish reasonable suspicion, the officer must only have “some indication that the motorist might have committed a crime,” as explained by

If the officer makes the stop and notices certain evidence that seems to support the drunk-driving suspicion (smelling of alcohol, slurred speech, etc.), he may choose to investigate further. This is where field sobriety tests and breathalyzer tests come into play. Failing one or both of these tests could be enough evidence to establish probable cause, which is what’s needed in order to arrest the allegedly drunk driver. The probable cause standard requires that “an officer must have enough evidence to suggest that the motorist has most likely committed a crime.”

Hopefully, readers now have a better understanding of how police officers make these decisions, as well as how defendants may be able to challenge them. An experienced criminal defense attorney can review the details of your arrest in order to determine if reasonable suspicion or probable cause may have been lacking.

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