The Fourth Amendment to the U.S. Constitution provides strong protections against unreasonable searches and seizures, which generally means those conducted without a court issued warrant. For this reason, an officer cannot stop a motor vehicle for no reason; but must generally have “reasonable suspicion” that unlawful activity is underway.
What is Reasonable Suspicion?
Reasonable suspicion is the belief that a person is breaking the law based on firsthand observations. In the case of a driving under the influence (DUI) case, this may mean that the driver is weaving, running traffic signals, or engaging in other behavior that indicates operating while impaired. However, an officer could not stop a vehicle just because it’s late at night, the car is near a bar and the officer guesses that the driver could have been drinking.
Sometimes police will use a pretext to make a stop and investigate for drunk driving. In a pretext stops a police officer will pull someone over a driver for an unrelated traffic infraction, even if the real reason for the stop was to determine if someone was intoxicated. This means that if the officer pulls someone over for a minor offense such as an incorrectly displayed license plate, and he or she then observes an open container of alcohol in the car or smells alcohol, the officer can then begin a DUI investigation. This has been approved by the U.S. Supreme Court, so long as there is reasonable suspicion of some illegality for the initial stop.
Exclusion of Evidence
Evidence acquired by police through unlawful searches can be excluded from trial. The fruit of the poisonous tree doctrine holds that any evidence derived from the unlawful search must also be be excluded. This means that even if a police officer uses a breathalyzer test on a suspect which demonstrates that the suspect was driving while severely intoxicated, that test will not be allowed as evidence at trial if the officer did not have reasonable suspicion to pull to car over in the first place.
Since there are not 100% clear rules for how strong a basis is required for ‘reasonable suspicion’ , defense attorneys will frequently seek to challenge officers; reasonable suspicion in making a traffic stop that ultimately lead to concrete evidence that their client was driving while intoxicated.
In the video that follows,defense counsel seeks to demonstrate that officers did not have reasonable suspicion that his client was violating the law, as needed to lawfully stop his car. The video shows direct and cross-examination of two witnesses, both police officers in the case. Other witnesses not featured in the clip include the defendants and a third police officer.[If outside of PRC, https://www.youtube.com/watch?v=o-B1S1ChzeI ]
Principle video translator Harry Zhang.