Can police use a traffic stop as a pretext to search for evidence?
As long as police have a valid reason to make a traffic stop, their "true" motives are irrelevant.
Judges generally ignore police officers’ subjective motivation when evaluating the legality of their conduct. If a police officer has a valid basis for detaining a motorist (even a nit-picky one like a broken taillight), the stop is valid no matter what the officer’s subjective purposes might be (Whren v. U.S., U.S. Sup. Ct. 1996; Arkansas v. Sullivan, U.S. Sup. Ct. 2001). However, police officers cannot search a car without a warrant based only on a traffic violation unless they have reason to believe that the car contains a weapon or evidence of crime that someone other than the driver might dispose of (Arizona v. Gant, U.S. Sup. Ct. 2009).
Example: Officer Colombo sees an old, battered car being driven at night by an unkempt driver in a wealthy section of town, and suspects that the driver might be planning to commit a crime. The officer notices that the light over the car’s rear license plate isn’t illuminated. The officer uses that minor traffic violation as an excuse to pull the car over and sees illegal drugs on the passenger seat. Officer Colombo then arrests the driver for possession of illegal drugs. The arrest and seizure of the drugs was valid. Whatever his motivation, the minor infraction gave Officer Colombo the right to stop the vehicle. Seeing the drugs in plain view gave the officer the right to make the arrest.
This article was excerpted from The Criminal Law Handbook, by Paul Bergman, J.D., and Sara J. Berman, J.D.