On May 31, 1979, Drug Enforcement Agency officers noticed Charles Carney approach a youth who followed Carney into a motor home parked in a lot in downtown San Diego. The officer had received a tip that Carney was using the motor home to sell marijuana in exchange for sex. The officers kept the motor home under surveillance while the youth and Carney were inside. When the youth left the motor home, the officers approached the youth and confirmed that Carney gave the youth marijuana in exchange for allowing Carney sexual contacts. The officers knocked on the door of the motor home, identified themselves, and entered without a warrant or consent. They found marijuana, plastic bags, and a scale on the table. The officers arrested Carney for possession