Illinois v. Gates

Law-enforcement authorities need a valid warrant, or, in legal terms, a judicial writ, to search a citizen's home or person. Such guarantees, enshrined by the Constitution, are considered cornerstones of a free, non-totalitarian society. In some instances, searches and seizures do occur without a proper writ, or have been granted under spurious grounds by judges, but any evidence obtained with such invalid warrants is not admissible in a trial. This is called the "exclusionary rule," for it excludes any evidence of a crime from being presented by prosecutors, no matter how damaging.

In May of 1978, a letter arrived at the police department of Bloomingdale, Illinois. The anonymous writer alleged that Bloomingdale residents Lance and Sue Gates were selling drugs from their home. The letter also provided a date on which the couple would travel to and return from Florida separately in order to ferry another shipment of contraband to their home for resale. Police investigated the Gates and their whereabouts, and confirmed that Lance Gates had flown to Florida and stayed in a motel room registered to his wife. Further inquiries revealed that Gates and an unidentified woman left the motel in a car with license plates registered to Gates, but for a different vehicle. With these details, Bloomingdale police obtained a warrant to search both the Gates residence as well as the car upon its arrival. They found 350 pounds of marijuana in the trunk of the car, and inside the house, more drugs and an unregistered firearm.