There are two main legal concepts that the police apply in a criminal investigation
to determine whether to detain someone, search and seize evidence, or
arrest someone: reasonable suspicion and probable cause. While these concepts
are used interchangeable, different circumstances must be met in order
to establish each one.
Law enforcement officials must first establish reasonable suspicion to
conduct an “investigatory” stop. An investigatory stop includes
a traffic stop on the road, stopping a person while walking, and frisking
or patting someone down for weapons.
In order to make such a stop, there must be certain circumstances or facts
evident that a crime is being committed, has been committed, or will be
committed. For example, if an officer on the highway witnesses another
driver speeding, driving without headlights on at night, or swerving from
one lane to another without signally, the officer has reasonable suspicion
that the driver is driving while intoxicated (based on the officer’s
training and experience).
During an investigatory stop, the police must then establish probable cause
to make an arrest, obtain a warrant, or search and seize evidence from
the scene of the alleged crime. The main difference between reasonable
suspicion and probable cause is that the standard for probable cause is
met if any reasonable person might believe someone is engaged in criminal
activity, while the standard for reasonable suspicion is met if any reasonable
officer might suspect criminal activity.
Going back to the example above, if an officer notices that the driver
smells like alcohol, has bloodshot eyes, or has difficulty moving or responding
to questions, then the officer has a probable cause because any reasonable
person would believe the driver is under the influence and make a
DUI arrest.
Without establishing these two legal concepts, any evidence gathered at
the scene is inadmissible at trial, which will likely result in the dismissal
of the entire case.
