A police officer only needs to believe he or she has smelled marijuana, in order to restrain a person through stop or arrest. An officer can perform an invasive search of the arrested individual, even if the basis for arrest is a probable cause like marijuana odor. If an officer detects marijuana odor from a vehicle, the officer does not even need to arrest in order to conduct a stop and search. If an officer suspects that marijuana odor is present in a room, the suspicion could supply probable cause for a more extensive search than would otherwise be acceptable.
To examine how reliable the often-used officer smell test actually is, researchers replicated real-life circumstances experienced by police and analyzed the accuracy for humans to discern marijuana odor in these situations. The researchers based the replicated circumstances on common court cases where officers justified their searches by claiming to have smelled marijuana. The results of the empirical studies cast severe doubt on the reliability of officer marijuana smell-tests. In the first study, the researchers recreated a situation in where, during a normal traffic stop, an officer would say he detects the odor of packaged marijuana, through the driver’s window, located in the trunk of a car. The study discovered that individuals in this officer’s position would not be able to accurately detect marijuana odor, due, at least partly, to the entrenching presence of diesel fumes.
In the second study, researchers analyzed a situation where officers would claim they discerned marijuana odor through chimney fumes of diesel exhaust originating from a marijuana grow room. The study found that individuals in these officers’ position would be incapable of detecting marijuana odor when such odor is mixed with diesel exhaust fumes in a ratio modeled from a actual growing situation in an marijuana grow room. This failure to reliably detect marijuana was nearly absolute, even in regards to individuals who are familiar with marijuana odor.